ipv6: Remove redundant route flushing during namespace dismantle

By the time fib6_net_exit() is executed all the netdevs in the namespace
have been either unregistered or pushed back to the default namespace.
That is because pernet subsys operations are always ordered before
pernet device operations and therefore invoked after them during
namespace dismantle.

Thus, all the routing tables in the namespace are empty by the time
fib6_net_exit() is invoked and the call to rt6_ifdown() can be removed.

This allows us to simplify the condition in fib6_ifdown() as it's only
ever called with an actual netdev.
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_fib.c

@@ -2103,7 +2103,6 @@ static void fib6_net_exit(struct net *net)
 {
 	unsigned int i;
 
-	rt6_ifdown(net, NULL);
 	del_timer_sync(&net->ipv6.ip6_fib_timer);
 
 	for (i = 0; i < FIB6_TABLE_HASHSZ; i++) {

net/ipv6/route.c

@@ -3470,10 +3470,9 @@ static int fib6_ifdown(struct rt6_info *rt, void *arg)
 	const struct arg_dev_net *adn = arg;
 	const struct net_device *dev = adn->dev;
 
-	if ((rt->dst.dev == dev || !dev) &&
+	if (rt->dst.dev == dev &&
 	    rt != adn->net->ipv6.ip6_null_entry &&
-	    (rt->rt6i_nsiblings == 0 ||
-	     (dev && netdev_unregistering(dev)) ||
+	    (rt->rt6i_nsiblings == 0 || netdev_unregistering(dev) ||
 	     !rt->rt6i_idev->cnf.ignore_routes_with_linkdown))
 		return -1;
 
@@ -3488,7 +3487,6 @@ void rt6_ifdown(struct net *net, struct net_device *dev)
 	};
 
 	fib6_clean_all(net, fib6_ifdown, &adn);
-	if (dev)
 	rt6_uncached_list_flush_dev(net, dev);
 }