ipv6/route: Don't match on fc_nh_id if not set in ip6_route_del()

If fc_nh_id isn't set, we shouldn't try to match against it. This
actually matters just for the RTF_CACHE below (where this case is
already handled): if iproute2 gets a route exception and tries to
delete it, it won't reference it by fc_nh_id, even if a nexthop
object might be associated to the originating route.

Fixes: 5b98324e ("ipv6: Allow routes to use nexthop objects")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -3840,7 +3840,8 @@ static int ip6_route_del(struct fib6_config *cfg,
 		for_each_fib6_node_rt_rcu(fn) {
 			struct fib6_nh *nh;
 
-			if (rt->nh && rt->nh->id != cfg->fc_nh_id)
+			if (rt->nh && cfg->fc_nh_id &&
+			    rt->nh->id != cfg->fc_nh_id)
 				continue;
 
 			if (cfg->fc_flags & RTF_CACHE) {