nvme-tcp: fix premature queue removal and I/O failover

nvme-tcp: fix premature queue removal and I/O failover

This patch addresses a data corruption issue observed in nvme-tcp during
testing.

In an NVMe native multipath setup, when an I/O timeout occurs, all
inflight I/Os are canceled almost immediately after the kernel socket is
shut down. These canceled I/Os are reported as host path errors,
triggering a failover that succeeds on a different path.

However, at this point, the original I/O may still be outstanding in the
host's network transmission path (e.g., the NIC’s TX queue). From the
user-space app's perspective, the buffer associated with the I/O is
considered completed since they're acked on the different path and may
be reused for new I/O requests.

Because nvme-tcp enables zero-copy by default in the transmission path,
this can lead to corrupted data being sent to the original target,
ultimately causing data corruption.

We can reproduce this data corruption by injecting delay on one path and
triggering i/o timeout.

To prevent this issue, this change ensures that all inflight
transmissions are fully completed from host's perspective before
returning from queue stop. To handle concurrent I/O timeout from multiple
namespaces under the same controller, always wait in queue stop
regardless of queue's state.

This aligns with the behavior of queue stopping in other NVMe fabric
transports.

Fixes: 3f2304f8c6d6 ("nvme-tcp: add NVMe over TCP host driver")
Signed-off-by: Michael Liang <mliang@purestorage.com>
Reviewed-by: Mohamed Khalfella <mkhalfella@purestorage.com>
Reviewed-by: Randy Jennings <randyj@purestorage.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>