nexthop: Fix attribute checking for groups

For nexthop groups, attributes after NHA_GROUP_TYPE are invalid, but
nh_check_attr_group starts checking at NHA_GROUP. The group type defaults
to multipath and the NHA_GROUP_TYPE is currently optional so this has
slipped through so far. Fix the attribute checking to handle support of
new group types.

Fixes: 430a049 ("nexthop: Add support for nexthop groups")
Signed-off-by: ASSOGBA Emery <assogba.emery@gmail.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/nexthop.c

@@ -433,7 +433,7 @@ static int nh_check_attr_group(struct net *net, struct nlattr *tb[],
 		if (!valid_group_nh(nh, len, extack))
 			return -EINVAL;
 	}
-	for (i = NHA_GROUP + 1; i < __NHA_MAX; ++i) {
+	for (i = NHA_GROUP_TYPE + 1; i < __NHA_MAX; ++i) {
 		if (!tb[i])
 			continue;