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>
diff --git a/drivers/net/wireless/zd1201.c b/drivers/net/wireless/zd1201.c
index 1e2b684..ece86a5 100644
--- a/drivers/net/wireless/zd1201.c
+++ b/drivers/net/wireless/zd1201.c
@@ -827,7 +827,6 @@
 	} else {
 		dev->stats.tx_packets++;
 		dev->stats.tx_bytes += skb->len;
-		dev->trans_start = jiffies;
 	}
 	kfree_skb(skb);
 
@@ -845,7 +844,7 @@
 	usb_unlink_urb(zd->tx_urb);
 	dev->stats.tx_errors++;
 	/* Restart the timeout to quiet the watchdog: */
-	dev->trans_start = jiffies;
+	dev->trans_start = jiffies; /* prevent tx timeout */
 }
 
 static int zd1201_set_mac_address(struct net_device *dev, void *p)