scsi: lpfc: Fix issuing init_vpi mbox on SLI-3 card

The driver is inadvertently trying to issue an INIT_VPI mailbox command on
an SLI-3 driver. The command is specific to SLI-4. When the call is made to
send the command, if on an SLI-3 adapter, an array pointer is NULL and the
driver will oops.

Fix by restricting the command to SLI-4 adapters only.

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>