k8s: Don't bother to create CEP if endpoint is already disconnecting
k8s: Don't bother to create CEP if endpoint is already disconnecting

A common pattern is that an entire namespcae is deleted while pods are still
being created. This will trigger a lot of errors like the one below. Fix this
by not even bothering to create a CEP if the endpoint is already disconnecting
again. This will not completely avoid the error but make it less likely.

```
level=error msg="Cannot create CEP" containerID=1c0bc02ec5 controller="sync-to-k8s-ciliumendpoint (1032)" datapathPolicyRevision=43 desiredPolicyRevision=43 endpointID=1032 error="ciliumendpoints.cilium.io \"client2\" is forbidden: unable to create new content in namespace staging-couchdb because it is being terminated" identity=25422 ipv4= ipv6= k8sPodName=staging-couchdb/client2 subsys=endpointsynchronizer
```

Signed-off-by: Thomas Graf <5f50a84c1fa3bcff146405017f36aec1a10a9e38@cilium.io>

cilium/cilium,cilium/cilium,tklauser/cilium,tgraf/cilium,michi-covalent/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,tgraf/cilium,cilium/cilium,tgraf/cilium,tklauser/cilium,cilium-team/cilium,tklauser/cilium,tklauser/cilium,cilium/cilium,tgraf/cilium,cilium-team/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,michi-covalent/cilium,tgraf/cilium