[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/zatm.c b/drivers/atm/zatm.c
index 85fee95..c4b75ec 100644
--- a/drivers/atm/zatm.c
+++ b/drivers/atm/zatm.c
@@ -400,7 +400,7 @@
 EVENT("error code 0x%x/0x%x\n",(here[3] & uPD98401_AAL5_ES) >>
   uPD98401_AAL5_ES_SHIFT,error);
 		skb = ((struct rx_buffer_head *) bus_to_virt(here[2]))->skb;
-		do_gettimeofday(&skb->stamp);
+		__net_timestamp(skb);
 #if 0
 printk("[-3..0] 0x%08lx 0x%08lx 0x%08lx 0x%08lx\n",((unsigned *) skb->data)[-3],
   ((unsigned *) skb->data)[-2],((unsigned *) skb->data)[-1],