[Bluetooth] Use try_module_get() for RFCOMM sessions

It is not possible to use __module_get() when adding a new RFCOMM
session, because there is a case where no reference count is hold.
This happens when the module is not in use right now and an incoming
connection occurs.

net/bluetooth/rfcomm/core.c

@@ -480,15 +480,16 @@ struct rfcomm_session *rfcomm_session_add(struct socket *sock, int state)
 	s->mtu = RFCOMM_DEFAULT_MTU;
 	s->cfc = RFCOMM_CFC_UNKNOWN;
 
+	/* Do not increment module usage count for listening sessions.
+	 * Otherwise we won't be able to unload the module. */
+	if (state != BT_LISTEN)
+		if (!try_module_get(THIS_MODULE)) {
+			kfree(s);
+			return NULL;
+		}
+
 	list_add(&s->list, &session_list);
 
-	/* Do not increment module usage count for listeting sessions.
-	 * Otherwise we won't be able to unload the module.
-	 * Non listening session are added either by a socket or a TTYs
-	 * which means that we already hold refcount to this module.
-	 */
-	if (state != BT_LISTEN)
-		__module_get(THIS_MODULE);
 	return s;
 }