scsi: qla2xxx: Fix session state stuck in Get Port DB

This patch sets discovery state back to GNL (Get Name List) when session is
stuck at GPDB (Get Port DataBase). This will allow state machine to retry
login and move session state ahead in discovery.

Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>