treewide: replace ip6tables with ip6tables-legacy

package/gluon-iptables-clamp-mss-to-pmtu/Makefile

@@ -6,7 +6,7 @@ include ../gluon.mk
 
 define Package/$(PKG_NAME)
   TITLE:=This will establish a firewall rule to clamp the mss to pmtu on the mesh-vpn interface when the connection is towards 64:ff9b::/96
-  DEPENDS:= +ip6tables
+  DEPENDS:= +ip6tables-legacy
 endef
 
 define Package/$(PKG_NAME)/description

targets/generic

@@ -80,5 +80,5 @@ packages {
 	'-wpad-basic',
 	'-wpad-basic-wolfssl',
 	'gluon-core',
-	'ip6tables',
+	'ip6tables-legacy',
 }