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

[seckek]

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:

[xiaoheiccc]

BindAddress should be 0.0.0.0

[seckek]

Wouldn't 0.0.0.0 listen on all interfaces which is different to using only one interface? I don't think that the intention is for users to always use 0.0.0.0, otherwise why have the option to change the BindAddress