ipv6: Mark dead nexthops with appropriate flags

When a netdev is put administratively down or unregistered all the
nexthops using it as their nexthop device should be marked with the
'dead' and 'linkdown' flags.

Currently, when a route is dumped its nexthop device is tested and the
flags are set accordingly. A similar check is performed during route
lookup.

Instead, we can simply mark the nexthops based on netdev events and
avoid checking the netdev's state during route dump and lookup.
Signed-off-by: NIdo Schimmel <idosch@mellanox.com>
Acked-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -3473,8 +3473,10 @@ static int fib6_ifdown(struct rt6_info *rt, void *arg)
 	if (rt->dst.dev == dev &&
 	    rt != adn->net->ipv6.ip6_null_entry &&
 	    (rt->rt6i_nsiblings == 0 || netdev_unregistering(dev) ||
-	     !rt->rt6i_idev->cnf.ignore_routes_with_linkdown))
+	     !rt->rt6i_idev->cnf.ignore_routes_with_linkdown)) {
+		rt->rt6i_nh_flags |= (RTNH_F_DEAD | RTNH_F_LINKDOWN);
 		return -1;
+	}
 
 	return 0;
 }