Explicitely set the local IP for outgoing connections, if we're listening
on only one Hostname or IP (of a multi-IP machine). This makes sure our
peers see our outgoing connections coming from the same IP that we're
listening on when we have a specific HOST= configured.
For machines with more than one IP this avoids source-destination
mismatch errors when advertizing our peer. Resolveskyuupichan/electrumx#225