ipv4: fix forwarding for strict source routes

After the change "Adjust semantics of rt->rt_gateway"
(commit f8126f1d) rt_gateway can be 0 but ip_forward() compares
it directly with nexthop. What we want here is to check if traffic
is to directly connected nexthop and to fail if using gateway.
Signed-off-by: NJulian Anastasov <ja@ssi.bg>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/ip_forward.c

@@ -85,7 +85,7 @@ int ip_forward(struct sk_buff *skb)
 
 	rt = skb_rtable(skb);
 
-	if (opt->is_strictroute && opt->nexthop != rt->rt_gateway)
+	if (opt->is_strictroute && rt->rt_gateway)
 		goto sr_failed;
 
 	if (unlikely(skb->len > dst_mtu(&rt->dst) && !skb_is_gso(skb) &&