nvme-fcloop: fix port deletes and callbacks

Now that there are potentially long delays between when a remoteport or
targetport delete calls is made and when the callback occurs (dev_loss_tmo
timeout), no longer block in the delete routines and move the final nport
puts to the callbacks.

Moved the fcloop_nport_get/put/free routines to avoid forward declarations.

Ensure port_info structs used in registrations are nulled in case fields
are not set (ex: devloss_tmo values).

Signed-off-by: James Smart <james.smart@broadcom.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>