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/irda/smsc-ircc2.c

@@ -868,7 +868,7 @@ static void smsc_ircc_timeout(struct net_device *dev)
 	spin_lock_irqsave(&self->lock, flags);
 	smsc_ircc_sir_start(self);
 	smsc_ircc_change_speed(self, self->io.speed);
-	dev->trans_start = jiffies;
+	dev->trans_start = jiffies; /* prevent tx timeout */
 	netif_wake_queue(dev);
 	spin_unlock_irqrestore(&self->lock, flags);
 }