scsi: qla2xxx: Fix duplicate switch's Nport ID entries

Current code relies on switch to provide a unique combination of WWPN +
NPORTID to tract an FC port.  This patch tries to detect a case where switch
data base can get corrupted where multiple WWPNs can have the same Nport ID.
The 1st Nport ID on the list will be kept while the duplicate Nport ID will be
discarded.

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>