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

In the Linux kernel, the following vulnerability has been resolved:

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 c8efcc2589464ac7 ("workqueue: allow chained queueing during

destruction") does not allow such operation.

The check introduced by commit 877afadad2dce8aa ("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.