netdevice: add helper to update trans_start

trans_start exists twice:
- as member of net_device (legacy)
- as member of netdev_queue

In order to get rid of the legacy case, add a helper for the
dev->trans_update (this patch), then convert spots that do

dev->trans_start = jiffies

to use this helper (next patch).

This would then allow us to change the helper so that it updates the
trans_stamp of netdev queue 0 instead.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -3481,6 +3481,12 @@ static inline void txq_trans_update(struct netdev_queue *txq)
 		txq->trans_start = jiffies;
 }
 
+/* legacy drivers only, netdev_start_xmit() sets txq->trans_start */
+static inline void netif_trans_update(struct net_device *dev)
+{
+	dev->trans_start = jiffies;
+}
+
 /**
  *	netif_tx_lock - grab network device transmit lock
  *	@dev: network device