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/decnet/af_decnet.c b/net/decnet/af_decnet.c
index bccb388..a5e3a59 100644
--- a/net/decnet/af_decnet.c
+++ b/net/decnet/af_decnet.c
@@ -1075,6 +1075,7 @@
 	int err = 0;
 	unsigned char type;
 	long timeo = sock_rcvtimeo(sk, flags & O_NONBLOCK);
+	struct dst_entry *dst;
 
 	lock_sock(sk);
 
@@ -1102,8 +1103,9 @@
 	}
 	release_sock(sk);
 
-	dst_release(xchg(&newsk->sk_dst_cache, skb->dst));
-	skb->dst = NULL;
+	dst = skb_dst(skb);
+	dst_release(xchg(&newsk->sk_dst_cache, dst));
+	skb_dst_set(skb, NULL);
 
 	DN_SK(newsk)->state        = DN_CR;
 	DN_SK(newsk)->addrrem      = cb->src_port;