[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/horizon.c b/drivers/atm/horizon.c
index 924a2c8..0cded04 100644
--- a/drivers/atm/horizon.c
+++ b/drivers/atm/horizon.c
@@ -1034,7 +1034,7 @@
 	  struct atm_vcc * vcc = ATM_SKB(skb)->vcc;
 	  // VC layer stats
 	  atomic_inc(&vcc->stats->rx);
-	  do_gettimeofday(&skb->stamp);
+	  __net_timestamp(skb);
 	  // end of our responsability
 	  vcc->push (vcc, skb);
 	}