Bluetooth: RFCOMM: avoid socket lock inversion in listener cleanup

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: RFCOMM: avoid socket lock inversion in listener cleanup rfcomm_sock_cleanup_listen() closes unaccepted child sockets through rfcomm_sock_close(), which takes the child socket lock before rfcomm_dlc_close() acquires rfcomm_mutex. The RFCOMM worker takes these locks in reverse order while handling connections and DLC state changes, so lockdep reports a possible deadlock. Close dequeued children without taking their socket lock. The accept queue owns a reference to each child, and bt_accept_dequeue() locks the child while unlinking it and clearing its parent pointer. Dropping the child lock makes it important to prevent a concurrent rfcomm_connect_ind() from enqueueing a new child after cleanup observes an empty queue. Set a listening socket to BT_CLOSED while its lock is still held, before dropping the lock and draining the queue. The state check in rfcomm_connect_ind() then rejects new children once cleanup starts.