dht find connected peers

This PR extends the DHT to send information re: peer "connectedness".
This means that --upon resolving dht queries -- connected peers will
signal whether or not they are directly connected to the peer. this is
in preparation for mesh messaging, and our "STUN" for NAT traversal.
yeah, i wanted to be explicit here to make sure it matches `Message_ConnectionType_value`. This may not be the best idea, perhaps i should import those symbols.