[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/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index 4f9e11b..55dc42e 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -999,7 +999,7 @@
 
 	if (atomic_read(&hdev->promisc)) {
 		/* Time stamp */
-		do_gettimeofday(&skb->stamp);
+		__net_timestamp(skb);
 
 		hci_send_to_sock(hdev, skb);
 	}