[Bug] Dev branch - Covenant doesn't start if the listener interface is no longer available

**Feature Request or Bug**
Bug

**Describe the feature request or bug**
If a listener is configured for an interface that no longer exists (eg. tun0) Covenant is unable to start.

**To Reproduce**
Steps to reproduce the behavior:
1. Create a listener in covenant
2. Disable the interface the listener was using (eg. by using "ifconfig eth0 down")
3. Restart covenant
4. Observe the "Cannot assign requested address" error.

**Expected behavior**
Covenant should start without the affected listener.

**Screenshots**
Setting up the listener:

Removing the interface and restarting Covenant: