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/net/ipv4/udp.c b/net/ipv4/udp.c
index 7a1d1ce..8f4158d 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -328,7 +328,7 @@
 	if (unlikely(sk = skb_steal_sock(skb)))
 		return sk;
 	else
-		return __udp4_lib_lookup(dev_net(skb->dst->dev), iph->saddr, sport,
+		return __udp4_lib_lookup(dev_net(skb_dst(skb)->dev), iph->saddr, sport,
 					 iph->daddr, dport, inet_iif(skb),
 					 udptable);
 }
@@ -1237,7 +1237,7 @@
 	struct sock *sk;
 	struct udphdr *uh;
 	unsigned short ulen;
-	struct rtable *rt = (struct rtable*)skb->dst;
+	struct rtable *rt = skb_rtable(skb);
 	__be32 saddr, daddr;
 	struct net *net = dev_net(skb->dev);