net: skb_defer_rx_timestamp should check for phydev before setting up classify

This change makes it so that the call skb_defer_rx_timestamp will first
check for a phydev before going in and manipulating the skb->data and
skb->len values.  By doing this we can avoid unnecessary work on network
devices that don't support phydev.  As a result we reduce the total
instruction count needed to process this on most devices.

Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: Alexander Duyck

net/core/timestamping.c

@@ -60,11 +60,15 @@ bool skb_defer_rx_timestamp(struct sk_buff *skb)
 	struct phy_device *phydev;
 	unsigned int type;
 
+	if (!skb->dev || !skb->dev->phydev || !skb->dev->phydev->drv)
+		return false;
+
 	if (skb_headroom(skb) < ETH_HLEN)
 		return false;
+
 	__skb_push(skb, ETH_HLEN);
 
-	type = classify(skb);
+	type = ptp_classify_raw(skb);
 
 	__skb_pull(skb, ETH_HLEN);