[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/ipx/af_ipx.c b/net/ipx/af_ipx.c
index 39d5939..c54f8ac 100644
--- a/net/ipx/af_ipx.c
+++ b/net/ipx/af_ipx.c
@@ -1796,8 +1796,8 @@
 				     copied);
 	if (rc)
 		goto out_free;
-	if (skb->stamp.tv_sec)
-		sk->sk_stamp = skb->stamp;
+	if (skb->tstamp.off_sec)
+		skb_get_timestamp(skb, &sk->sk_stamp)
 
 	msg->msg_namelen = sizeof(*sipx);