nvme-tcp: always fail a request when sending it failed

queue stoppage and inflight requests cancellation is fully fenced from
io_work and thus failing a request from this context. Hence we don't
need to try to guess from the socket retcode if this failure is because
the queue is about to be torn down or not.

We are perfectly safe to just fail it, the request will not be cancelled
later on.

This solves possible very long shutdown delays when the users issues a
'nvme disconnect-all'

Reported-by: Daniel Wagner <dwagner@suse.de>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>