[Bluetooth] Fix reference counting for incoming connections

The L2CAP reference counting must be increased by the RFCOMM module if an
incoming connection is accepted. If this is not done, it will be decreased
one time to often if the connection is terminated.

net/bluetooth/rfcomm/core.c

@@ -1650,6 +1650,8 @@ static inline void rfcomm_accept_connection(struct rfcomm_session *s)
 	nsock->type = sock->type;
 	nsock->ops  = sock->ops;
 
+	__module_get(nsock->ops->owner);
+
 	err = sock->ops->accept(sock, nsock, O_NONBLOCK);
 	if (err < 0) {
 		sock_release(nsock);