ublk: quiesce request queue when aborting queue

So far aborting queue ends request when the ubq daemon is exiting, and
it can be run concurrently with ublk_queue_rq(), this way is fragile and
we depend on the tricky usage of UBLK_IO_FLAG_ABORTED for avoiding such
race.

Quiesce queue when aborting queue, and the two code paths can be run
completely exclusively, then it becomes easier to add new ublk feature,
such as relaxing single same task limit for each queue.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20231009093324.957829-6-ming.lei@redhat.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>