ipv4: Kill rt->rt_oif

Never actually used.

It was being set on output routes to the original OIF specified in the
flow key used for the lookup.

Adjust the only user, ipmr_rt_fib_lookup(), for greater correctness of
the flowi4_oif and flowi4_iif values, thanks to feedback from Julian
Anastasov.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index eee3bf6..8eec8f4 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1795,8 +1795,11 @@
 		.daddr = iph->daddr,
 		.saddr = iph->saddr,
 		.flowi4_tos = RT_TOS(iph->tos),
-		.flowi4_oif = rt->rt_oif,
-		.flowi4_iif = rt->rt_iif,
+		.flowi4_oif = (rt_is_output_route(rt) ?
+			       skb->dev->ifindex : 0),
+		.flowi4_iif = (rt_is_output_route(rt) ?
+			       net->loopback_dev->ifindex :
+			       skb->dev->ifindex),
 		.flowi4_mark = skb->mark,
 	};
 	struct mr_table *mrt;