ipv4: Turn rt->rt_route_iif into rt->rt_is_input.

That is this value's only use, as a boolean to indicate whether
a route is an input route or not.

So implement it that way, using a u16 gap present in the struct
already.

Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/xfrm4_policy.c

@@ -79,7 +79,6 @@ static int xfrm4_fill_dst(struct xfrm_dst *xdst, struct net_device *dev,
 	struct rtable *rt = (struct rtable *)xdst->route;
 	const struct flowi4 *fl4 = &fl->u.ip4;
 
-	xdst->u.rt.rt_route_iif = fl4->flowi4_iif;
 	xdst->u.rt.rt_iif = fl4->flowi4_iif;
 
 	xdst->u.dst.dev = dev;
@@ -87,6 +86,7 @@ static int xfrm4_fill_dst(struct xfrm_dst *xdst, struct net_device *dev,
 
 	/* Sheit... I remember I did this right. Apparently,
 	 * it was magically lost, so this code needs audit */
+	xdst->u.rt.rt_is_input = rt->rt_is_input;
 	xdst->u.rt.rt_flags = rt->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST |
 					      RTCF_LOCAL);
 	xdst->u.rt.rt_type = rt->rt_type;