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/bfin_mac.c b/drivers/net/bfin_mac.c
index c488cea..b0207f0 100644
--- a/drivers/net/bfin_mac.c
+++ b/drivers/net/bfin_mac.c
@@ -654,7 +654,6 @@
 out:
 	adjust_tx_list();
 	current_tx_ptr = current_tx_ptr->next;
-	dev->trans_start = jiffies;
 	dev->stats.tx_packets++;
 	dev->stats.tx_bytes += (skb->len);
 	return NETDEV_TX_OK;
@@ -805,7 +804,7 @@
 	bfin_mac_enable();
 
 	/* We can accept TX packets again */
-	dev->trans_start = jiffies;
+	dev->trans_start = jiffies; /* prevent tx timeout */
 	netif_wake_queue(dev);
 }