usbnet: fix crash due to missing BQL accounting after resume

In commit 7ff14c5 ("usbnet: Add support for Byte Queue Limits
(BQL)"), it was missed that usbnet_resume() enqueues SKBs using
__skb_queue_tail() without reporting them to BQL. As a result, the next
call to netdev_completed_queue() triggers a BUG_ON() in dql_completed(),
since the SKBs queued during resume were never accounted for.

This patch fixes the issue by adding a corresponding netdev_sent_queue()
call in usbnet_resume() when SKBs are queued after suspend. Because
dev->txq.lock is held at this point, no concurrent calls to
netdev_sent_queue() from usbnet_start_xmit() can occur.

The crash can be reproduced by generating network traffic
(e.g. iperf3 -c ... -t 0), suspending the system, and then waking it up
(e.g. rtcwake -m mem -s 5).

When testing USB2 Android tethering, the system crashed within three
suspend/resume cycles without this patch. With the patch applied, no
crashes were observed after 90 cycles.

Reported-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Tested-by: Simon Schippers <simon.schippers@tu-dortmund.de>
Signed-off-by: Simon Schippers <simon.schippers@tu-dortmund.de>

Author: simoschip2000

drivers/net/usb/usbnet.c

@@ -1984,6 +1984,7 @@ int usbnet_resume(struct usb_interface *intf)
 			} else {
 				netif_trans_update(dev->net);
 				__skb_queue_tail(&dev->txq, skb);
+				netdev_sent_queue(dev->net, skb->len);
 			}
 		}