scsi: libfc: Implement RTV responder

The libfc stack generates an RTV request, so we should be implementing
an RTV responder, too.

Signed-off-by: Hannes Reinecke <hare@suse.com>
Acked-by: Johannes Thumshirn <jth@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>