ipv4: fix TCP early demux

commit 92101b3b2e317 (ipv4: Prepare for change of rt->rt_iif encoding.)
invalidated TCP early demux, because rx_dst_ifindex is not properly
initialized and checked.

Also remove the use of inet_iif(skb) in favor or skb->skb_iif

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 5912ac3..3f1cc20 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -388,6 +388,7 @@
 		struct tcp_cookie_values *oldcvp = oldtp->cookie_values;
 
 		newsk->sk_rx_dst = dst_clone(skb_dst(skb));
+		inet_sk(newsk)->rx_dst_ifindex = skb->skb_iif;
 
 		/* TCP Cookie Transactions require space for the cookie pair,
 		 * as it differs for each connection.  There is no need to