[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/ambassador.c b/drivers/atm/ambassador.c
index 73c6b85..d74a7c5 100644
--- a/drivers/atm/ambassador.c
+++ b/drivers/atm/ambassador.c
@@ -513,7 +513,7 @@
 	  
 	  // VC layer stats
 	  atomic_inc(&atm_vcc->stats->rx);
-	  do_gettimeofday(&skb->stamp);
+	  __net_timestamp(skb);
 	  // end of our responsability
 	  atm_vcc->push (atm_vcc, skb);
 	  return;