[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/sctp/input.c b/net/sctp/input.c
index 742be91..28f3224 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -236,8 +236,8 @@
 	}
 
 	/* SCTP seems to always need a timestamp right now (FIXME) */
-	if (skb->stamp.tv_sec == 0) {
-		do_gettimeofday(&skb->stamp);
+	if (skb->tstamp.off_sec == 0) {
+		__net_timestamp(skb);
 		sock_enable_timestamp(sk); 
 	}