r6040: enable transmit time stamping.

This patch enables software (and phy device) transmit time stamping
for the RDC R6040 Fast Ethernet MAC. Compile tested only.

Cc: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Richard Cochran <richard.cochran@omicron.at>
Signed-off-by: David S. Miller <davem@conan.davemloft.net>

drivers/net/r6040.c

@@ -846,6 +846,8 @@ static netdev_tx_t r6040_start_xmit(struct sk_buff *skb,
 
 	spin_unlock_irqrestore(&lp->lock, flags);
 
+	skb_tx_timestamp(skb);
+
 	return NETDEV_TX_OK;
 }