VOIP Call not working on different network connection.

### Steps to reproduce

Related: https://github.com/vector-im/element-ios/issues/3059

Scenario 1:

```
Device 1 5G/LTE <-----> router <-----> Synapse Server
Device 2 5G/LTE <--|
```
Calling between Device 1 and Device 2 **works**.

Scenario 2:

```
router <-----> Synapse Server
|--> Device 1 (WiFi)
|--> Device 2 (WiFi)
```
Calling between Device 1 and Device 2 **works**.

Scenario 3:
```
Device 1 5G/LTE <-----> router <-----> Synapse Server
|--> Device 2 (WiFi)
```

Synapse Server and Device 2 are under the same LAN, e.g. Server is 10.0.0.2, Device 2 is 10.0.0.5
Calling between Device 1 and Device 2 **does not work**. The App always show "Call Connecting..."

Scenario 4:

```
router <-----> Synapse Server
|--> Device 1 (WiFi) behind Windscribe VPN
|--> Device 2 (WiFi)
```
Calling between Device 1 and Device 2 **does not work**. The App always show "Call Connecting..."

Scenario 5:

```
router <-----> Synapse Server
|--> Device 1 (WiFi) behind Windscribe VPN
|--> Device 2 (WiFi) behind Windscribe VPN
```
Calling between Device 1 and Device 2 **does not work**. The App always show "Call Connecting..."

Scenario 6:

```
Device 1 5G/LTE behind Windscribe VPN <-----> router <-----> Synapse Server
Device 2 5G/LTE behind Windscribe VPN <--|
```
Calling between Device 1 and Device 2 **does not work**. The App always show "Call Connecting..."

Scenario 7:

```
Device 1 5G/LTE behind Windscribe VPN <-----> router <-----> Synapse Server
Device 2 5G/LTE <--|
```
Calling between Device 1 and Device 2 **does not work**. The App always show "Call Connecting..."

More info:
In my homeserver.yaml:
```
turn_uris: [ "turns:staticauth.openrelay.metered.ca:443" ]
turn_shared_secret: "openrelayprojectsecret"
turn_allow_guests: true
```
I am using TURN server from https://www.metered.ca/tools/openrelay/
I tried to host my own coturn server, the result is exactly the same as above.

### Outcome

#### What did you expect?
VOIP should work under what ever network condition
#### What happened instead?
VOIP work only under certain condition.

### Your phone model

Moto G100, Xiaomi 12X, Mi Pad 5 with ArrowOS 13.0

### Operating system version

Android 12

### Application version and app store

Element 1.5.7 from both Google Play and from F-droid

### Homeserver

Synapse 1.71

### Will you send logs?

No

### Are you willing to provide a PR?

No