ipv6: Only emit append events for appended routes

Current code will emit an append event in the FIB notification chain for
any route added with NLM_F_APPEND set, even if the route was not
appended to any existing route.

This is inconsistent with IPv4 where such an event is only emitted when
the new route is appended after an existing one.

Align IPv6 behavior with IPv4, thereby allowing listeners to more easily
handle these events.

Fixes: f34436a4 ("net/ipv6: Simplify route replace and appending into multipath route")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_fib.c

@@ -934,6 +934,7 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct fib6_info *rt,
 {
 	struct fib6_info *leaf = rcu_dereference_protected(fn->leaf,
 				    lockdep_is_held(&rt->fib6_table->tb6_lock));
+	enum fib_event_type event = FIB_EVENT_ENTRY_ADD;
 	struct fib6_info *iter = NULL, *match = NULL;
 	struct fib6_info __rcu **ins;
 	int replace = (info->nlh &&
@@ -1013,6 +1014,7 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct fib6_info *rt,
 				       "Can not append to a REJECT route");
 			return -EINVAL;
 		}
+		event = FIB_EVENT_ENTRY_APPEND;
 		rt->fib6_nsiblings = match->fib6_nsiblings;
 		list_add_tail(&rt->fib6_siblings, &match->fib6_siblings);
 		match->fib6_nsiblings++;
@@ -1034,15 +1036,12 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct fib6_info *rt,
 	 *	insert node
 	 */
 	if (!replace) {
-		enum fib_event_type event;
-
 		if (!add)
 			pr_warn("NLM_F_CREATE should be set when creating new route\n");
 
 add:
 		nlflags |= NLM_F_CREATE;
 
-		event = append ? FIB_EVENT_ENTRY_APPEND : FIB_EVENT_ENTRY_ADD;
 		err = call_fib6_entry_notifiers(info->nl_net, event, rt,
 						extack);
 		if (err)