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/tokenring/smctr.c

@@ -4562,7 +4562,7 @@ static void smctr_timeout(struct net_device *dev)
          * fake transmission time and go on trying. Our own timeout
          * routine is in sktr_timer_chk()
          */
-        dev->trans_start = jiffies;
+        dev->trans_start = jiffies; /* prevent tx timeout */
         netif_wake_queue(dev);
 }