can: gs_usb: fix busy loop if no more TX context is available

If sending messages with no cable connected, it quickly happens that
there is no more TX context available. Then "gs_can_start_xmit()"
returns with "NETDEV_TX_BUSY" and the upper layer does retry
immediately keeping the CPU busy. To fix that issue, I moved
"atomic_dec(&dev->active_tx_urbs)" from "gs_usb_xmit_callback()" to
the TX done handling in "gs_usb_receive_bulk_callback()". Renaming
"active_tx_urbs" to "active_tx_contexts" and moving it into
"gs_[alloc|free]_tx_context()" would also make sense.

Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/gs_usb.c

@@ -375,6 +375,8 @@ static void gs_usb_receive_bulk_callback(struct urb *urb)
 
 		gs_free_tx_context(txc);
 
+		atomic_dec(&dev->active_tx_urbs);
+
 		netif_wake_queue(netdev);
 	}
 
@@ -463,14 +465,6 @@ static void gs_usb_xmit_callback(struct urb *urb)
 			  urb->transfer_buffer_length,
 			  urb->transfer_buffer,
 			  urb->transfer_dma);
-
-	atomic_dec(&dev->active_tx_urbs);
-
-	if (!netif_device_present(netdev))
-		return;
-
-	if (netif_queue_stopped(netdev))
-		netif_wake_queue(netdev);
 }
 
 static netdev_tx_t gs_can_start_xmit(struct sk_buff *skb,