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/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index ea37741..53b6a41 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -981,9 +981,10 @@
 	struct tcphdr *th = tcp_hdr(skb), *t1;
 	struct sk_buff *buff;
 	struct flowi fl;
-	struct net *net = dev_net(skb->dst->dev);
+	struct net *net = dev_net(skb_dst(skb)->dev);
 	struct sock *ctl_sk = net->ipv6.tcp_sk;
 	unsigned int tot_len = sizeof(struct tcphdr);
+	struct dst_entry *dst;
 	__be32 *topt;
 
 	if (ts)
@@ -1052,8 +1053,9 @@
 	 * Underlying function will use this to retrieve the network
 	 * namespace
 	 */
-	if (!ip6_dst_lookup(ctl_sk, &buff->dst, &fl)) {
-		if (xfrm_lookup(net, &buff->dst, &fl, NULL, 0) >= 0) {
+	if (!ip6_dst_lookup(ctl_sk, &dst, &fl)) {
+		if (xfrm_lookup(net, &dst, &fl, NULL, 0) >= 0) {
+			skb_dst_set(buff, dst);
 			ip6_xmit(ctl_sk, buff, &fl, NULL, 0);
 			TCP_INC_STATS_BH(net, TCP_MIB_OUTSEGS);
 			if (rst)