Protofamily

Nope, I don't think this will work.  `open` has always had the potential to throw an `IOException` but now we have a different situation; an unsupported family.  This should result in a `CommandFailed(bind)` but it's not going to here.  What you're going to get (most likely) is the death of the `UdpListener` after it's supervisor has given up trying to restart it.  

However, it should be an easy fix. See line 51/55 below for an example.