ip_tunnel: Use mark in skb by default

This allows marks set by connmark in iptables
to be used for route lookups.

Signed-off-by: Thomas Winter <thomas.winter@alliedtelesis.co.nz>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ip_tunnel.c

@@ -711,9 +711,16 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev,
 		}
 	}
 
-	init_tunnel_flow(&fl4, protocol, dst, tnl_params->saddr,
-			 tunnel->parms.o_key, RT_TOS(tos), tunnel->parms.link,
-			 tunnel->fwmark);
+	if (tunnel->fwmark) {
+		init_tunnel_flow(&fl4, protocol, dst, tnl_params->saddr,
+				 tunnel->parms.o_key, RT_TOS(tos), tunnel->parms.link,
+				 tunnel->fwmark);
+	}
+	else {
+		init_tunnel_flow(&fl4, protocol, dst, tnl_params->saddr,
+				 tunnel->parms.o_key, RT_TOS(tos), tunnel->parms.link,
+				 skb->mark);
+	}
 
 	if (ip_tunnel_encap(skb, tunnel, &protocol, &fl4) < 0)
 		goto tx_error;