[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/idt77252.c b/drivers/atm/idt77252.c
index 30b7e99..b4a76ca 100644
--- a/drivers/atm/idt77252.c
+++ b/drivers/atm/idt77252.c
@@ -1101,7 +1101,7 @@
 			       cell, ATM_CELL_PAYLOAD);
 
 			ATM_SKB(sb)->vcc = vcc;
-			do_gettimeofday(&sb->stamp);
+			__net_timestamp(sb);
 			vcc->push(vcc, sb);
 			atomic_inc(&vcc->stats->rx);
 
@@ -1179,7 +1179,7 @@
 
 			skb_trim(skb, len);
 			ATM_SKB(skb)->vcc = vcc;
-			do_gettimeofday(&skb->stamp);
+			__net_timestamp(skb);
 
 			vcc->push(vcc, skb);
 			atomic_inc(&vcc->stats->rx);
@@ -1201,7 +1201,7 @@
 
 		skb_trim(skb, len);
 		ATM_SKB(skb)->vcc = vcc;
-		do_gettimeofday(&skb->stamp);
+		__net_timestamp(skb);
 
 		vcc->push(vcc, skb);
 		atomic_inc(&vcc->stats->rx);
@@ -1340,7 +1340,7 @@
 		       ATM_CELL_PAYLOAD);
 
 		ATM_SKB(sb)->vcc = vcc;
-		do_gettimeofday(&sb->stamp);
+		__net_timestamp(sb);
 		vcc->push(vcc, sb);
 		atomic_inc(&vcc->stats->rx);