scsi: qla2xxx: Fix setting lower transfer speed if GPSC fails

This patch prevents driver from setting lower default speed of 1 GB/sec,
if the switch does not support Get Port Speed Capabilities (GPSC)
command. Setting this default speed results into much lower write
performance for large sequential WRITE.  This patch modifies driver to
check for gpsc_supported flags and prevents driver from issuing
MBC_SET_PORT_PARAM (001Ah) to set default speed of 1 GB/sec. If driver
does not send this mailbox command, firmware assumes maximum supported
link speed and will operate at the max speed.

Cc: stable@vger.kernel.org
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Reported-by: Eda Zhou <ezhou@redhat.com>
Reviewed-by: Ewan D. Milne <emilne@redhat.com>
Tested-by: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>