tcp: Handle TCP SYN+ACK/ACK/RST transparency

The TCP stack sends out SYN+ACK/ACK/RST reply packets in response to
incoming packets. The non-local source address check on output bites
us again, as replies for transparently redirected traffic won't have a
chance to leave the node.

This patch selectively sets the FLOWI_FLAG_ANYSRC flag when doing the
route lookup for those replies. Transparent replies are enabled if the
listening socket has the transparent socket flag set.

Signed-off-by: KOVACS Krisztian <hidden@sch.bme.hu>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index 139b78b..dced3f6 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -72,7 +72,8 @@
 				sack_ok	   : 1,
 				wscale_ok  : 1,
 				ecn_ok	   : 1,
-				acked	   : 1;
+				acked	   : 1,
+				no_srccheck: 1;
 	struct ip_options	*opt;
 };
 
@@ -204,4 +205,9 @@
 	return req;
 }
 
+static inline __u8 inet_sk_flowi_flags(const struct sock *sk)
+{
+	return inet_sk(sk)->transparent ? FLOWI_FLAG_ANYSRC : 0;
+}
+
 #endif	/* _INET_SOCK_H */