nvmet: force reconnect when number of queue changes

In order to test queue number changes we need to make sure that the
host reconnects. Because only when the host disconnects from the
target the number of queues are allowed to change according the spec.

The initial idea was to disable and re-enable the ports and have the
host wait until the KATO timer expires, triggering error
recovery. Though the host would see a DNR reply when trying to
reconnect. Because of the DNR bit the connection is dropped
completely. There is no point in trying to reconnect with the same
parameters according the spec.

We can force to reconnect the host is by deleting all controllers. The
host will observe any newly posted request to fail and thus starts the
error recovery but this time without the DNR bit set.

Signed-off-by: Daniel Wagner <dwagner@suse.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Acked-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>