net: skb->dst accessors

Define three accessors to get/set dst attached to a skb

struct dst_entry *skb_dst(const struct sk_buff *skb)

void skb_dst_set(struct sk_buff *skb, struct dst_entry *dst)

void skb_dst_drop(struct sk_buff *skb)
This one should replace occurrences of :
dst_release(skb->dst)
skb->dst = NULL;

Delete skb->dst field

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 2e9f5c0..736bca4 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -994,7 +994,7 @@
 		return __xfrm_policy_check(sk, ndir, skb, family);
 
 	return	(!net->xfrm.policy_count[dir] && !skb->sp) ||
-		(skb->dst->flags & DST_NOPOLICY) ||
+		(skb_dst(skb)->flags & DST_NOPOLICY) ||
 		__xfrm_policy_check(sk, ndir, skb, family);
 }
 
@@ -1048,7 +1048,7 @@
 	struct net *net = dev_net(skb->dev);
 
 	return	!net->xfrm.policy_count[XFRM_POLICY_OUT] ||
-		(skb->dst->flags & DST_NOXFRM) ||
+		(skb_dst(skb)->flags & DST_NOXFRM) ||
 		__xfrm_route_forward(skb, family);
 }