scsi: target: core: New key must be used for moved PR

scsi: target: core: New key must be used for moved PR

According to SPC4 5.12.8:

  e) Retain the reservation key specified in the SERVICE ACTION RESERVATION
  KEY field and associated information;

But currently sa_res_key is only used for the not existing I_T nexus. Add a
changing of the key for the existing I_T nexus the PR moved to.

Link: https://lore.kernel.org/r/20220909090425.14479-5-d.bogdanov@yadro.com
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>