nixos-module/server/lxc-containers: resolve lxc interface name issue by ensuring the type key comes first

it took very long to find this

nix/nixos-module/server/lxc-containers.nix

@@ -1,16 +1,6 @@
 { hostName, self, config, lib, pkgs, ... }:
 
 let
-  # Downgrade: lxc-4.0.9 names network interfaces in containers eth0,
-  # and eth1 despite configured differently.
-  lxc = pkgs.lxc.overrideAttrs (_: rec {
-    version = "4.0.6";
-    src = pkgs.fetchurl {
-      url = "https://linuxcontainers.org/downloads/lxc/lxc-${version}.tar.gz";
-      sha256 = "0qz4l7mlhq7hx53q606qgvkyzyr01glsw290v8ppzvxn1fydlrci";
-    };
-  });
-
   # Containers that are run on this host
   containers =
     lib.filterAttrs (_: { role, model, ... }:
@@ -54,12 +44,17 @@ let
         })
       ) (builtins.attrNames interfaces);
 
+      attrNamesOrdered = attrs:
+        if attrs ? type
+        then [ "type" ] ++ lib.remove "type" (builtins.attrNames attrs)
+        else builtins.attrNames attrs;
+
       serialize = name: x:
         if builtins.isString x
         then "${name} = ${x}\n"
         else if builtins.isAttrs x
         then builtins.concatStringsSep "" (
-          map (n: serialize "${name}.${n}" x.${n}) (builtins.attrNames x)
+          map (n: serialize "${name}.${n}" x.${n}) (attrNamesOrdered x)
         )
         else if builtins.isList x
         then
@@ -176,7 +171,7 @@ in
 
   environment.systemPackages = [
     # `lxc-attach` et al
-    lxc build-script
+    pkgs.lxc build-script
     # User scripts
     enable-script disable-script
   ];
@@ -234,14 +229,14 @@ in
       "/var/lib/lxc/%i/rootfs/init"
       "/etc/start-containers"
     ];
-    serviceConfig = {
+    serviceConfig = with pkgs; {
       Type = "simple";
       ExecStart = "${lxc}/bin/lxc-start -F -C -n %i";
       ExecStop = "${lxc}/bin/lxc-stop -n %i";
       ExecReload =
         let
-          script = pkgs.writeScript "reload-lxc-container.sh" ''
-            #! ${pkgs.runtimeShell} -e
+          script = writeScript "reload-lxc-container.sh" ''
+            #! ${runtimeShell} -e
 
             SYSTEM=$(dirname $(readlink /var/lib/lxc/$1/rootfs/init))
             exec ${lxc}/bin/lxc-attach -n $1 $SYSTEM/bin/switch-to-configuration switch