scsi: target: core: Use RTPI from target port

Replace all references to RTPI from LUN field to se_portal_group field.  It
introduces consistent reporting of RTPI for all LUNs and all target ports.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Link: https://lore.kernel.org/r/20230301084512.21956-3-d.bogdanov@yadro.com


Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>