Bluetooth: coredump: Quiesce dump work on unregister

hci_devcd_handle_pkt_init() arms dump_timeout and coredump producers
queue dump_rx without holding an hdev reference. Unregister leaves both
works live, so disconnecting during an active dump lets them access hdev
after hci_release_dev() frees it.

Shut down coredump processing during unregister. Close the producer gate
under dump_q.lock before disabling both works, then free the active buffer
and queued packets under hci_dev_lock. Serializing the gate with enqueue
prevents controller-specific workers from adding packets after the final
purge.

Fixes: 9695ef876fd1 ("Bluetooth: Add support for hci devcoredump")
Reported-by: syzbot+b170dbf55520ebf5969a@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b170dbf55520ebf5969a
Reported-by: Aby Sam Ross <abysamross@gmail.com>
Link: https://lore.kernel.org/r/20260322210849.68743-1-abysamross@gmail.com
Suggested-by: Aby Sam Ross <abysamross@gmail.com>
Reported-by: Tristan Madani <tristan@talencesecurity.com>
Link: https://lore.kernel.org/r/20260814231248.3096377-1-tristmd@gmail.com
Reported-by: Xiang Mei <xmei5@asu.edu>
Assisted-by: OpenAI Codex:gpt-5
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>