macb: enable transmit time stamping.

This patch enables software (and phy device) transmit time stamping
Compile tested only.

Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: NRichard Cochran <richard.cochran@omicron.at>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/macb.c

@@ -670,6 +670,8 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	entry = NEXT_TX(entry);
 	bp->tx_head = entry;
 
+	skb_tx_timestamp(skb);
+
 	macb_writel(bp, NCR, macb_readl(bp, NCR) | MACB_BIT(TSTART));
 
 	if (TX_BUFFS_AVAIL(bp) < 1)