[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/drivers/atm/atmtcp.c b/drivers/atm/atmtcp.c
index f2f01cb..57f1810 100644
--- a/drivers/atm/atmtcp.c
+++ b/drivers/atm/atmtcp.c
@@ -325,7 +325,7 @@
 		result = -ENOBUFS;
 		goto done;
 	}
-	do_gettimeofday(&new_skb->stamp);
+	__net_timestamp(new_skb);
 	memcpy(skb_put(new_skb,skb->len),skb->data,skb->len);
 	out_vcc->push(out_vcc,new_skb);
 	atomic_inc(&vcc->stats->tx);