nixos/pihole-ftl: fix openFirewall ports (#424348)

nixos/modules/services/networking/pihole-ftl.md

···
 {
   services.pihole-ftl = {
     enable = true;
+    openFirewallDNS = true;
     openFirewallDHCP = true;
     queryLogDeleter.enable = true;
     lists = [

nixos/modules/services/networking/pihole-ftl.nix

···
       example = "3";
     };
 
+    openFirewallDNS = mkOption {
+      type = types.bool;
+      default = false;
+      description = "Open ports in the firewall for pihole-FTL's DNS server.";
+    };
+
     openFirewallDHCP = mkOption {
       type = types.bool;
       default = false;
···
     };
 
     networking.firewall = lib.mkMerge [
-      (mkIf cfg.openFirewallDHCP {
+      (mkIf cfg.openFirewallDNS {
         allowedUDPPorts = [ 53 ];
         allowedTCPPorts = [ 53 ];
+      })
+
+      (mkIf cfg.openFirewallDHCP {
+        allowedUDPPorts = [ 67 ];
       })
 
       (mkIf cfg.openFirewallWebserver {