Allow biding sshd to specified addresses.

Also :port is supported by sshd. You my want to listen on:
```
Port 123
Port 124
ListenAddress ip
ListenAddress :125
```

That will make it listen on ip:123, ip:124 and *:125. I don't see any reason to limit the configuration this way. I'd change the assertion with `addr != null || port != null`.