ipv6: Restore RTF_ADDRCONF check in rt6_qualify_for_ecmp

The RTF_ADDRCONF flag filters out routes added by RA's in determining
which routes can be appended to an existing one to create a multipath
route. Restore the flag check and add a comment to document the RA piece.

Fixes: 4e54507a ("ipv6: Simplify rt6_qualify_for_ecmp")
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c

@@ -4928,7 +4928,7 @@ static void mlxsw_sp_rt6_destroy(struct mlxsw_sp_rt6 *mlxsw_sp_rt6)
 static bool mlxsw_sp_fib6_rt_can_mp(const struct fib6_info *rt)
 {
 	/* RTF_CACHE routes are ignored */
-	return rt->fib6_nh.fib_nh_gw_family;
+	return !(rt->fib6_flags & RTF_ADDRCONF) && rt->fib6_nh.fib_nh_gw_family;
 }
 
 static struct fib6_info *

include/net/ip6_route.h

@@ -68,7 +68,9 @@ static inline bool rt6_need_strict(const struct in6_addr *daddr)
 
 static inline bool rt6_qualify_for_ecmp(const struct fib6_info *f6i)
 {
-	return f6i->fib6_nh.fib_nh_gw_family;
+	/* the RTF_ADDRCONF flag filters out RA's */
+	return !(f6i->fib6_flags & RTF_ADDRCONF) &&
+		f6i->fib6_nh.fib_nh_gw_family;
 }
 
 void ip6_route_input(struct sk_buff *skb);