The external address of the IGD might not be always routable if
the router is not directly connected to the internet.
So we need to always add the published address returned by the DHT even if UPNP
is enabled and actif. Failing to do so, and if the peer use only relay candidates,
the TURN will reject all incoming connections from our public address because
it were not in the candidates list and thus not authorized by TURN.

The automatic reallocation of failing mappings was also improved.

Change-Id: I5fb1424d5dc61b990595c229be647099b017eba1
Gitlab: #335