airfield: fix build

Airfield suffered from loose version constraints which
caused severe version (and API) conflicts between its dependencies
and transitive ones.

Furthermore the `npm2nix` packaging is deprecated and needed to be
replaced by `node2nix`.

see #31032

pkgs/tools/networking/airfield/node.nix

@@ -0,0 +1,16 @@
+# This file has been generated by node2nix 1.4.0. Do not edit!
+
+{pkgs ? import <nixpkgs> {
+    inherit system;
+  }, system ? builtins.currentSystem, nodejs ? pkgs."nodejs-6_x"}:
+
+let
+  nodeEnv = import ../../../development/node-packages/node-env.nix {
+    inherit (pkgs) stdenv python2 utillinux runCommand writeTextFile;
+    inherit nodejs;
+  };
+in
+import ./node-packages.nix {
+  inherit (pkgs) fetchurl fetchgit;
+  inherit nodeEnv;
+}