Fix a system performance issue created by ata_sort_queue(). This function

Fix a system performance issue created by ata_sort_queue().  This function
implements an elevator sort but it also allows requests to be delayed
indefinitely when other requests continually get inserted in front of them.
HAMMER's almost log-linear writing really exposes this issue.

The fix is to count how many times a request got delayed due to an insertion.
If the count exceeds 8, the new request is placed at the end of the queue and
set as the new freeze point.