nvme-rdma: stop queues instead of simply flipping their state

If we move the queues from LIVE state, we might as well stop them (drain
for rdma).  Do it after we stop the request queues to prevent a stray
request sneaking in .queue_rq after we stop the queue.

Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>