scsi: lpfc: Cap NPIV vports to 256

Depending on the chipset, the number of NPIV vports may vary and be in
excess of what most switches support (256). To avoid confusion with the
users, limit the reported NPIV vports to 256.

Additionally correct the 16G adapter which is reporting a bogus NPIV vport
number if the link is down.

Signed-off-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>