containers: make all variables explicit

Instead of merging the argument set just make all arguments explicit.

nix/os/containers/mailserver.nix

@@ -1,12 +1,13 @@
-{ ... } @ args:
+{ hostAddress
+, localAddress
+, imapsPort ? 993
+, sievePort ? 4190
+}:
 
 let
   passwords = import ../../variables/passwords.crypt.nix;
 
-in
-{ imapsPort ? 993
-, sievePort ? 4190
-}: args // {
+in {
 
   config = { pkgs, ... }: {
     imports = [
@@ -158,4 +159,6 @@ in
       protocol = "tcp";
     }
   ];
+
+  inherit hostAddress localAddress;
 }