An aoe device's rq_list contains accepted block requests that are
waiting to be transmitted to the aoe target. This queue was added as
part of the conversion to blk_mq. However, the queue was not cleaned out
when an aoe device is downed which caused blk_mq_freeze_queue() to sleep
indefinitely waiting for those requests to complete, causing a hang. This
fix cleans out the queue before calling blk_mq_freeze_queue().
Link: https://bugzilla.kernel.org/show_bug.cgi?id=212665
Fixes: 3582dd291788 ("aoe: convert aoeblk to blk-mq")
Signed-off-by: Justin Sanders <jsanders.devel@xxxxxxxxx>