mesh-vpn-core: require legacy iptables

Require legacy iptables, as Gluon still depends on firewall3. Otherwise,
nftables is pulled in as a dependency.

package/gluon-mesh-vpn-core/Makefile

@@ -6,7 +6,7 @@ include ../gluon.mk
 
 define Package/gluon-mesh-vpn-core
   TITLE:=Basic support for connecting meshes via VPN tunnels
-  DEPENDS:=+gluon-core +gluon-wan-dnsmasq +iptables +iptables-mod-extra +simple-tc
+  DEPENDS:=+gluon-core +gluon-wan-dnsmasq +iptables-legacy +iptables-mod-extra +simple-tc
   USERID:=:gluon-mesh-vpn=800
 endef