TLS passthrough Gateway and TLSRoute to SSL-enabled PostgreSQL instance not working

*Description*:
>What issue is being seen?
I expected to be able to connect from the outside to an exposed PostgreSQL instance through my newly defined **TLS-passthrough Gateway** and my **TLSRoute**

Instead, I received a **server closed the connection unexpectedly* immediately after trying to connect

```bash
root@d31b66b2a97c:/# psql -h store.fsmn.xyz -p 6432 -U myuser mydatabase
psql: error: connection to server at "store.fsmn.xyz" (10.111.9.116), port 6432 failed: server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
```

I'm working with a VPN, hence I can reach even Gateways with private IPs (my Kubernetes clusters is an Azure AKS one).

I can still reach the same PostgreSQL instance through a **TCP-enabled Gateway** and **TCPRoute** (their configurations are shown below).

```bash
root@d31b66b2a97c:/# psql -h store.fsmn.xyz -p 5432 -U us_contributor m9sweeper
Password for user us_contributor:
psql (15.8 (Debian 15.8-0+deb12u1), server 15.3 (OnGres 15.3-build-6.30))
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, compression: off)
Type "help" for help.

m9sweeper=>
```

*Repro steps*:
> Include sample requests, environment, etc. All data and inputs
required to reproduce the bug.

Below you can find my *EnvoyProxy*, *GatewayClass*, *Gateway* and *TLSRoute*

```yaml
---
apiVersion: gateway.envoyproxy.io/v1alpha1
kind: EnvoyProxy
metadata:
name: eg
namespace: envoy-gateway-system
spec:
mergeGateways: true
routingType: Service
logging:
level:
default: debug
provider:
type: Kubernetes
kubernetes:
envoyDeployment:
replicas: 1
container:
resources:
requests:
cpu: 150m
memory: 500Mi
limits:
cpu: 150m
memory: 500Mi
# perchè Azure capisca se deve creare un LoadBalancer "privato" o con IP pubblicogi
envoyService:
annotations:
service.beta.kubernetes.io/azure-load-balancer-internal: "true"
service.beta.kubernetes.io/azure-load-balancer-ipv4: 10.111.9.116
```

```yaml
---
apiVersion: gateway.networking.k8s.io/v1
kind: GatewayClass
metadata:
name: eg
spec:
controllerName: gateway.envoyproxy.io/gatewayclass-controller
parametersRef:
group: gateway.envoyproxy.io
kind: EnvoyProxy
name: eg
namespace: envoy-gateway-system
```

```yaml
---
apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
name: test-fsmn-xyz-stackgres-tls
namespace: default
spec:
gatewayClassName: eg
listeners:
- name: stackgres
protocol: TLS
port: 6432
allowedRoutes:
kinds:
- kind: TLSRoute
namespaces:
from: All
tls:
mode: Passthrough
```

```yaml
---
apiVersion: gateway.networking.k8s.io/v1alpha2
kind: TLSRoute
metadata:
name: tlsroute-store
namespace: stackgres-dev
spec:
parentRefs:
- name: test-fsmn-xyz-stackgres-tls
namespace: default
hostnames:
- "store.fsmn.xyz"
rules:
- backendRefs:
- group: ""
kind: Service
name: store
port: 5432
weight: 1
```

>**Note**: If there are privacy concerns, sanitize the data prior to
sharing.

*Environment*:
>Include the environment like gateway version, envoy version and so on.

I'm using Helm to install Envoy Gateway, the Helm Chart version is **v1.1.2**
My Kubernetes cluster is an Azure AKS

This other combination of TCP-enabled Gateway and TCPRoute allows me to reach the PostgreSQL instance correctly.

```yaml
---
apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
name: test-fsmn-xyz-stackgres
namespace: stackgres-dev
spec:
gatewayClassName: eg
listeners:
- name: stackgres
protocol: TCP
port: 5432
allowedRoutes:
kinds:
- kind: TCPRoute
```

```yaml
---
apiVersion: gateway.networking.k8s.io/v1alpha2
kind: TCPRoute
metadata:
name: stackgres-dev-store
namespace: stackgres-dev
spec:
parentRefs:
- name: test-fsmn-xyz-stackgres
sectionName: stackgres
rules:
- backendRefs:
- group: ""
kind: Service
name: store
port: 5432
```

**I had exactly the same results (TLSRoute unreachable, server closed the connection unexpectedly) when I tried to follow the tutorial [here](https://gateway.envoyproxy.io/docs/tasks/security/tls-passthrough/)

*Logs*:
>Include the access logs and the Envoy logs.

Each time I try to connect through the TLS passthrough gateway and TLSRoute I see no log entries (even with **debug** set for log verbosity)

Here are the **kubectl describe** outputs for both my TLSRoute and TLS-passthrough enabled Gateway.

```bash
k describe tlsroute -n stackgres-dev
Name: tlsroute-store
Namespace: stackgres-dev
Labels:
Annotations:
API Version: gateway.networking.k8s.io/v1alpha2
Kind: TLSRoute
Metadata:
Creation Timestamp: 2024-10-31T10:10:10Z
Generation: 1
Resource Version: 295799376
UID: 2364d608-b703-480c-bd9e-9b861cb5d3aa
Spec:
Hostnames:
store.fsmn.xyz
Parent Refs:
Group: gateway.networking.k8s.io
Kind: Gateway
Name: test-fsmn-xyz-stackgres-tls
Namespace: default
Rules:
Backend Refs:
Group:
Kind: Service
Name: store
Port: 5432
Weight: 1
Status:
Parents:
Conditions:
Last Transition Time: 2024-10-31T10:10:10Z
Message: Route is accepted
Observed Generation: 1
Reason: Accepted
Status: True
Type: Accepted
Last Transition Time: 2024-10-31T10:10:10Z
Message: Resolved all the Object references for the Route
Observed Generation: 1
Reason: ResolvedRefs
Status: True
Type: ResolvedRefs
Controller Name: gateway.envoyproxy.io/gatewayclass-controller
Parent Ref:
Group: gateway.networking.k8s.io
Kind: Gateway
Name: test-fsmn-xyz-stackgres-tls
Namespace: default
Events:
```

```bash
k describe gateway/test-fsmn-xyz-stackgres-tls
Name: test-fsmn-xyz-stackgres-tls
Namespace: default
Labels:
Annotations:
API Version: gateway.networking.k8s.io/v1
Kind: Gateway
Metadata:
Creation Timestamp: 2024-10-31T10:06:26Z
Generation: 2
Resource Version: 295799375
UID: a2b58ba0-ef3a-46ab-ad23-223850934a63
Spec:
Gateway Class Name: eg
Listeners:
Allowed Routes:
Kinds:
Group: gateway.networking.k8s.io
Kind: TLSRoute
Namespaces:
From: All
Name: stackgres
Port: 6432
Protocol: TLS
Tls:
Mode: Passthrough
Status:
Addresses:
Type: IPAddress
Value: 10.111.9.116
Conditions:
Last Transition Time: 2024-10-31T10:10:10Z
Message: The Gateway has been scheduled by Envoy Gateway
Observed Generation: 2
Reason: Accepted
Status: True
Type: Accepted
Last Transition Time: 2024-10-31T10:10:10Z
Message: Address assigned to the Gateway, 1/1 envoy Deployment replicas available
Observed Generation: 2
Reason: Programmed
Status: True
Type: Programmed
Listeners:
Attached Routes: 1
Conditions:
Last Transition Time: 2024-10-31T10:10:10Z
Message: Sending translated listener configuration to the data plane
Observed Generation: 2
Reason: Programmed
Status: True
Type: Programmed
Last Transition Time: 2024-10-31T10:10:10Z
Message: Listener has been successfully translated
Observed Generation: 2
Reason: Accepted
Status: True
Type: Accepted
Last Transition Time: 2024-10-31T10:10:10Z
Message: Listener references have been resolved
Observed Generation: 2
Reason: ResolvedRefs
Status: True
Type: ResolvedRefs
Name: stackgres
Supported Kinds:
Group: gateway.networking.k8s.io
Kind: TLSRoute
Events:
```