When connecting to a TURN server, the peer needs to authorize ours candidates
to access to that server. This check existed, but not at the good place.
Indeed, the connection' status is given by ice_sess_on_peer_connection, not
by the first message we send (because the first message is sent when
the connection already exists).
I still don't have any clue why this problem was frequent only for the first
connection between two peers.