MFC r330954, r330955 (by imp):
When tearing down a queue pair, also delete the queue entries.

The NVME standard has required in section 7.2.6, since at least 1.1,
that a clean shutdown is signalled by deleting the subission and the
completion queues before setting the shutdown bit in CC. The 1.0
standard, apparently, did not and many of the early Intel cards didn't
care. Some newer cards care, at least one whose beta firmware can
scramble the card on an unclean shutdown. Linux has done this for some
time. To make it possible to move forward with an evaluation of this
pre-release card with wonky firmware, delete the queues on the card
when we delete the qpair structures.