ipv4: Change rt->rt_iif encoding.

On input packet processing, rt->rt_iif will be zero if we should
use skb->dev->ifindex.

Since we access rt->rt_iif consistently via inet_iif(), that is
the only spot whose interpretation have to adjust.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/route.h

@@ -277,7 +277,11 @@ static inline struct rtable *ip_route_newports(struct flowi4 *fl4, struct rtable
 
 static inline int inet_iif(const struct sk_buff *skb)
 {
-	return skb_rtable(skb)->rt_iif;
+	int iif = skb_rtable(skb)->rt_iif;
+
+	if (iif)
+		return iif;
+	return skb->skb_iif;
 }
 
 extern int sysctl_ip_default_ttl;

net/ipv4/route.c

@@ -1309,7 +1309,7 @@ static int ip_route_input_mc(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 	rth->rt_flags	= RTCF_MULTICAST;
 	rth->rt_type	= RTN_MULTICAST;
 	rth->rt_is_input= 1;
-	rth->rt_iif	= dev->ifindex;
+	rth->rt_iif	= 0;
 	rth->rt_pmtu	= 0;
 	rth->rt_gateway	= 0;
 	if (our) {
@@ -1435,7 +1435,7 @@ static int __mkroute_input(struct sk_buff *skb,
 	rth->rt_flags = flags;
 	rth->rt_type = res->type;
 	rth->rt_is_input = 1;
-	rth->rt_iif 	= in_dev->dev->ifindex;
+	rth->rt_iif 	= 0;
 	rth->rt_pmtu	= 0;
 	rth->rt_gateway	= 0;
 
@@ -1608,7 +1608,7 @@ out:	return err;
 	rth->rt_flags 	= flags|RTCF_LOCAL;
 	rth->rt_type	= res.type;
 	rth->rt_is_input = 1;
-	rth->rt_iif	= dev->ifindex;
+	rth->rt_iif	= 0;
 	rth->rt_pmtu	= 0;
 	rth->rt_gateway	= 0;
 	if (res.type == RTN_UNREACHABLE) {
@@ -1772,7 +1772,7 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
 	rth->rt_flags	= flags;
 	rth->rt_type	= type;
 	rth->rt_is_input = 0;
-	rth->rt_iif	= orig_oif ? : dev_out->ifindex;
+	rth->rt_iif	= orig_oif ? : 0;
 	rth->rt_pmtu	= 0;
 	rth->rt_gateway = 0;