scsi: qla2xxx: Fix driver unload by shutting down chip

Use chip shutdown at the start of unload to stop all DMA + traffic and
bring down the laser. This prevents any link activities from triggering the
driver to be re-engaged.

Fixes: 4b60c827

 ("scsi: qla2xxx: Add fw_started flags to qpair")
Cc: <stable@vger.kernel.org> #4.16
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>