libtorc-core: Fix peer removal when Bonjour is not active on the peer.

- if a peer does not advertise itself, but is searching and detects and
connects to this instance, the peer reference needs to be deleted when
the socket disconnects.
- this will be further complicated when upnp is finished as their will
be multiple sources for a peer reference, which may then disappear
independantly (i.e. the client may disable UPnP).
- so track the sources that have detected this peer and only delete when
no active (as opposed to passive) detection methods recognise it.