[NET]: skb_get/set_timestamp use const

The new timestamp get/set routines should have const attribute
on parameters (helps to indicate direction).
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -1251,7 +1251,7 @@ extern void skb_add_mtu(int mtu);
  *	This function converts the offset back to a struct timeval and stores
  *	it in stamp.
  */
-static inline void skb_get_timestamp(struct sk_buff *skb, struct timeval *stamp)
+static inline void skb_get_timestamp(const struct sk_buff *skb, struct timeval *stamp)
 {
 	stamp->tv_sec  = skb->tstamp.off_sec;
 	stamp->tv_usec = skb->tstamp.off_usec;
@@ -1270,7 +1270,7 @@ static inline void skb_get_timestamp(struct sk_buff *skb, struct timeval *stamp)
  *	This function converts a struct timeval to an offset and stores
  *	it in the skb.
  */
-static inline void skb_set_timestamp(struct sk_buff *skb, struct timeval *stamp)
+static inline void skb_set_timestamp(struct sk_buff *skb, const struct timeval *stamp)
 {
 	skb->tstamp.off_sec  = stamp->tv_sec - skb_tv_base.tv_sec;
 	skb->tstamp.off_usec = stamp->tv_usec - skb_tv_base.tv_usec;