net/ipv6: Revert attempt to simplify route replace and append

NetworkManager likes to manage linklocal prefix routes and does so with
the NLM_F_APPEND flag, breaking attempts to simplify the IPv6 route
code and by extension enable multipath routes with device only nexthops.

Revert f34436a43092 and these followup patches:
6eba08c3626b ("ipv6: Only emit append events for appended routes").
ce45bded6435 ("mlxsw: spectrum_router: Align with new route replace logic")
53b562df8c20 ("mlxsw: spectrum_router: Allow appending to dev-only routes")

Update the fib_tests cases to reflect the old behavior.

Fixes: f34436a43092 ("net/ipv6: Simplify route replace and appending into multipath route")
Signed-off-by: David Ahern <dsahern@gmail.com>
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 86a0e43..63f9941 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -3842,7 +3842,7 @@ static struct fib6_info *rt6_multipath_first_sibling(const struct fib6_info *rt)
 			lockdep_is_held(&rt->fib6_table->tb6_lock));
 	while (iter) {
 		if (iter->fib6_metric == rt->fib6_metric &&
-		    iter->fib6_nsiblings)
+		    rt6_qualify_for_ecmp(iter))
 			return iter;
 		iter = rcu_dereference_protected(iter->fib6_next,
 				lockdep_is_held(&rt->fib6_table->tb6_lock));
@@ -4439,7 +4439,6 @@ static int ip6_route_multipath_add(struct fib6_config *cfg,
 		 */
 		cfg->fc_nlinfo.nlh->nlmsg_flags &= ~(NLM_F_EXCL |
 						     NLM_F_REPLACE);
-		cfg->fc_nlinfo.nlh->nlmsg_flags |= NLM_F_APPEND;
 		nhn++;
 	}