Bluetooth Classic AVDTP: stale timeout work on signalling-channel disconnect leads to kernel timeout-list corruption

The AVDTP signalling layer arms a 6-second command timeout (AVDTP_TIMEOUT) in avdtp_send_cmd() whenever the local device issues an AVDTP request. Every response handler in subsys/bluetooth/host/classic/avdtp.c cancels session->timeout_work before clearing the pending request, but bt_avdtp_l2cap_disconnected() only cleared session->req and left the delayable work armed. The struct bt_avdtp session is the first member of struct bt_a2dp, whose instances live in a static per-connection array, and a2dp_get_connection() in subsys/bluetooth/host/classic/a2dp.c wipes a slot with memset() as soon as session->br_chan.chan.conn is NULL — which the L2CAP layer arranges immediately after the disconnect callback returns. A remote Bluetooth BR/EDR peer triggers the condition by opening the AVDTP signalling channel, letting the local application issue an AVDTP procedure (the standard A2DP flow issues bt_a2dp_discover() from the connected callback), then tearing the signalling channel down without responding and re-opening it within the remaining timeout window. The reconnect reaches a2dp_accept() → a2dp_get_connection(), which zeroes the whole struct bt_a2dp while the work item's struct _timeout is still linked into the kernel's global timeout list. Both the disconnect and the reconnect instants are chosen by the attacker, so no race has to be won; an encrypted BR/EDR link is required, and CONFIG_BT_A2DP (experimental) must be enabled. With the default CONFIG_TIMEOUT_BACKEND_DLIST backend th