It is possible to bypass the queue-proxy

/area networking

## What version of Knative?

v0.11.0-125-gb8f7090cc

## Expected Behavior

From within the cluster, it shouldn't be possible to connect directly to the user container and bypass the queue proxy for a revision.

I would expect that this would be prohibited, possibly via network policy.

## Actual Behavior

Port 8080 of the user container is exposed and available

Note: this only works if the revision is scaled to 1 or more instances already

## Steps to Reproduce the Problem

### Deploy a knative service ("webapp" in my example)

### get the PodIP

```
% kubectl get pods/webapp-mrpn8-deployment-6559dcff9b-c2pxx -oyaml | grep "podIP:"
podIP: 10.36.0.28
```

### Able to (from on cluster) connect directly to port 8080 on that pod

```
# curl http://10.36.0.28:8080

Hello there...

```

Start by reproducing the issue with the provided Kubernetes deployment, PodIP lookup, and curl request to port 8080. Trace how the revision's user-container networking is configured and evaluate the proposed network-policy approach; done means in-cluster access cannot bypass the queue proxy while normal revision traffic still works.

Written by the indexing model from the issue text.