scsi: qla2xxx: Increase ql2xmaxqdepth to 64

ql2xmaxqdepth is the module parameter that seeds the per target
queue depth in the Scsi midlayer (sdev->queue_depth). Performance
testing revealed that increasing this value would improve IOPS
numbers under certain workloads.

Signed-off-by: Michael Hernandez <michael.hernandez@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>