dst: Add __skb_dst_copy() variation

This variation on skb_dst_copy() doesn't require two skbs.
Signed-off-by: Joe Stringer <joestringer@nicira.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dst.h

@@ -289,13 +289,18 @@ static inline void skb_dst_drop(struct sk_buff *skb)
 	}
 }
 
-static inline void skb_dst_copy(struct sk_buff *nskb, const struct sk_buff *oskb)
+static inline void __skb_dst_copy(struct sk_buff *nskb, unsigned long refdst)
 {
-	nskb->_skb_refdst = oskb->_skb_refdst;
+	nskb->_skb_refdst = refdst;
 	if (!(nskb->_skb_refdst & SKB_DST_NOREF))
 		dst_clone(skb_dst(nskb));
 }
 
+static inline void skb_dst_copy(struct sk_buff *nskb, const struct sk_buff *oskb)
+{
+	__skb_dst_copy(nskb, oskb->_skb_refdst);
+}
+
 /**
  * skb_dst_force - makes sure skb dst is refcounted
  * @skb: buffer