Bluetooth: use hdev->workqueue when queuing hdev->{cmd,ncmd}_timer works

syzbot is reporting attempt to schedule hdev->cmd_work work from system_wq
WQ into hdev->workqueue WQ which is under draining operation [1], for
commit c8efcc25 ("workqueue: allow chained queueing during
destruction") does not allow such operation.

The check introduced by commit 877afada ("Bluetooth: When HCI work
queue is drained, only queue chained work") was incomplete.

Use hdev->workqueue WQ when queuing hdev->{cmd,ncmd}_timer works because
hci_{cmd,ncmd}_timeout() calls queue_work(hdev->workqueue). Also, protect
the queuing operation with RCU read lock in order to avoid calling
queue_delayed_work() after cancel_delayed_work() completed.

Link: https://syzkaller.appspot.com/bug?extid=243b7d89777f90f7613b

 [1]
Reported-by: syzbot <syzbot+243b7d89777f90f7613b@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Fixes: 877afada ("Bluetooth: When HCI work queue is drained, only queue chained work")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>