[NET]: Store skb->timestamp as offset to a base timestamp

Reduces skb size by 8 bytes on 64-bit.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index 1ac64c0..9e6e683 100644
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -533,7 +533,7 @@
  	if (skb->dev)
  		qp->iif = skb->dev->ifindex;
 	skb->dev = NULL;
-	qp->stamp = skb->stamp;
+	skb_get_timestamp(skb, &qp->stamp);
 	qp->meat += skb->len;
 	atomic_add(skb->truesize, &ip_frag_mem);
 	if (offset == 0)
@@ -615,7 +615,7 @@
 
 	head->next = NULL;
 	head->dev = dev;
-	head->stamp = qp->stamp;
+	skb_set_timestamp(head, &qp->stamp);
 
 	iph = head->nh.iph;
 	iph->frag_off = 0;