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/dccp/ipv4.c b/net/dccp/ipv4.c
index 2cf48ba..a0a36c9 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -507,7 +507,7 @@
 	const struct iphdr *rxiph;
 	struct sk_buff *skb;
 	struct dst_entry *dst;
-	struct net *net = dev_net(rxskb->dst->dev);
+	struct net *net = dev_net(skb_dst(rxskb)->dev);
 	struct sock *ctl_sk = net->dccp.v4_ctl_sk;
 
 	/* Never send a reset in response to a reset. */
@@ -528,7 +528,7 @@
 	rxiph = ip_hdr(rxskb);
 	dccp_hdr(skb)->dccph_checksum = dccp_v4_csum_finish(skb, rxiph->saddr,
 								 rxiph->daddr);
-	skb->dst = dst_clone(dst);
+	skb_dst_set(skb, dst_clone(dst));
 
 	bh_lock_sock(ctl_sk);
 	err = ip_build_and_send_pkt(skb, ctl_sk,