net: ipv6: fix TCP early demux

IPv6 needs a cookie in dst_check() call.

We need to add rx_dst_cookie and provide a family independent
sk_rx_dst_set(sk, skb) method to properly support IPv6 TCP early demux.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2fd2bc9..85308b9 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5392,6 +5392,8 @@
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
+	if (unlikely(sk->sk_rx_dst == NULL))
+		inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
 	/*
 	 *	Header prediction.
 	 *	The code loosely follows the one in the famous
@@ -5605,7 +5607,7 @@
 	tcp_set_state(sk, TCP_ESTABLISHED);
 
 	if (skb != NULL) {
-		inet_sk_rx_dst_set(sk, skb);
+		icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
 		security_inet_conn_established(sk, skb);
 	}