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/xfrm4_input.c b/net/ipv4/xfrm4_input.c
index 4ec2162..f9f922a 100644
--- a/net/ipv4/xfrm4_input.c
+++ b/net/ipv4/xfrm4_input.c
@@ -23,7 +23,7 @@
 
 static inline int xfrm4_rcv_encap_finish(struct sk_buff *skb)
 {
-	if (skb->dst == NULL) {
+	if (skb_dst(skb) == NULL) {
 		const struct iphdr *iph = ip_hdr(skb);
 
 		if (ip_route_input(skb, iph->daddr, iph->saddr, iph->tos,