Drop log-level of failure to listen to warn
Drop log-level of failure to listen to warn

* No version bump
* Failure to listen on a socket is Warn, not Error, because it's
  sufficiently common on systems which only support either IPv4 or IPv6
  but not both.  It's worth noting as more than Info, but it's not a
  serious error.  If we fail to listen on _any_ sockets, that's already
  coded to log Fatal a little later.

PennockTech/fingerd