nvme-fcloop: refactor to enable target to host LS

Currently nvmefc-loop only sends LS's from host to target.
Slightly rework data structures and routine names to reflect this
path. Allows a straight-forward conversion to be used by ls's
from target to host.

Signed-off-by: James Smart <jsmart2021@gmail.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>