USBNET: increase max rx/tx qlen for improving USB3 thoughtput

The default RX_QLEN()/TX_QLEN() didn't consider super speed
USB device, so only max 4 URBs are scheduled at the same time
for tx/rx, then USB3 NIC can't perform very well.

With this patch, both rx and tx thoughput are increased more than
100Mbps when doing iperf test on ax88179_178a USB 3.0 NIC.
Signed-off-by: NMing Lei <ming.lei@canonical.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/usb/usbnet.c

@@ -355,6 +355,15 @@ void usbnet_update_max_qlen(struct usbnet *dev)
 		dev->rx_qlen = MAX_QUEUE_MEMORY / dev->rx_urb_size;
 		dev->tx_qlen = MAX_QUEUE_MEMORY / dev->hard_mtu;
 		break;
+	case USB_SPEED_SUPER:
+		/*
+		 * Not take default 5ms qlen for super speed HC to
+		 * save memory, and iperf tests show 2.5ms qlen can
+		 * work well
+		 */
+		dev->rx_qlen = 5 * MAX_QUEUE_MEMORY / dev->rx_urb_size;
+		dev->tx_qlen = 5 * MAX_QUEUE_MEMORY / dev->hard_mtu;
+		break;
 	default:
 		dev->rx_qlen = dev->tx_qlen = 4;
 	}