scsi: libfc: Rework PRLI handling

PRLI is only required if the port is acting as an initiator; ports
which support target functionality only do not need to send PRLI.
At the same time the PRLI state is only used if the port initiated
a PRLI transfer; if we received a PRLI request we should _not_
change the state as this would cause our PRLI response to be dropped.
And when we receive a PRLI response we need to check if an image
pair has been established; if not the remote port cannot act as a
target for us and we need to disable target functionality.

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>