net: trans_start cleanups

Now that core network takes care of trans_start updates, dont do it
in drivers themselves, if possible. Drivers can avoid one cache miss
(on dev->trans_start) in their start_xmit() handler.

Exceptions are NETIF_F_LLTX drivers

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/pegasus.c

@@ -808,7 +808,7 @@ static void write_bulk_callback(struct urb *urb)
 		break;
 	}
 
-	net->trans_start = jiffies;
+	net->trans_start = jiffies; /* prevent tx timeout */
 	netif_wake_queue(net);
 }
 
@@ -909,7 +909,6 @@ static netdev_tx_t pegasus_start_xmit(struct sk_buff *skb,
 	} else {
 		pegasus->stats.tx_packets++;
 		pegasus->stats.tx_bytes += skb->len;
-		net->trans_start = jiffies;
 	}
 	dev_kfree_skb(skb);