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/smc91x.c b/drivers/net/smc91x.c
index 682bc4f..10cf0cb 100644
--- a/drivers/net/smc91x.c
+++ b/drivers/net/smc91x.c
@@ -1360,7 +1360,7 @@
 		schedule_work(&lp->phy_configure);
 
 	/* We can accept TX packets again */
-	dev->trans_start = jiffies;
+	dev->trans_start = jiffies; /* prevent tx timeout */
 	netif_wake_queue(dev);
 }