usbnet: consider device busy at each recieved packet

usbnet should centrally handle busy reporting in the rx path
so subdrivers need not worry. This hurts use cases which do
rx only or predominantly.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/usbnet.c

@@ -493,6 +493,7 @@ block:
 		if (netif_running (dev->net) &&
 		    !test_bit (EVENT_RX_HALT, &dev->flags)) {
 			rx_submit (dev, urb, GFP_ATOMIC);
+			usb_mark_last_busy(dev->udev);
 			return;
 		}
 		usb_free_urb (urb);