scsi: storvsc: Increase cmd_per_lun for higher speed devices

Increase cmd_per_lun to allow more I/Os in progress per device,
particularly for NVMe's.  The Hyper-V host side can handle the higher
count with no issues.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
Acked-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>