scsi: ibmvfc: Avoid loss of all paths during SVC node reboot

scsi: ibmvfc: Avoid loss of all paths during SVC node reboot

When an SVC node goes down as part of a node reboot, its WWPNs are moved to
the remaining node. When the node is back online, its WWPNs are moved
back. The result is that the WWPN moves from one NPort_ID to another, then
back again.  The ibmvfc driver was forcing the old port to be removed, but
not sending an implicit logout. When the WWPN showed up at the new
location, the PLOGI failed as there was already a login established for the
old scsi id. The patch below fixes this by ensuring we always send an
implicit logout for any scsi id associated with an rport prior to calling
fc_remote_port_delete.

Link: https://lore.kernel.org/r/1582767943-16611-1-git-send-email-brking@linux.vnet.ibm.com
Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>