WIP add zones to firewall module

- zones are an attrset of name -> [interface-service]

- the firewall will create empty "ifname" sets for each zone name
 in each address family (ip, ip6)

- then watch the interface services, and add the "ifname" outputs
to the corresponding sets when they appear

This commit only adds the empty sets

examples/rotuer.nix

@@ -69,6 +69,10 @@ in rec {
     firewall = {
       enable = true;
       rules = secrets.firewallRules;
+      zones = {
+        lan = [ config.services.int ];
+        wan = [ config.services.wan  ] ;
+      };
     };
     wireless.networks = {
       # EDIT: if you have more or fewer wireless radios, here is where