nixos/hardware/rtl-sdr: new module

This is a very thin module to ensure "plugdev" user exists and some udev
rules are enabled, a prerequisite for using rtl-sdr.

nixos/modules/hardware/rtl-sdr.nix

@@ -0,0 +1,20 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.hardware.rtl-sdr;
+
+in {
+  options.hardware.rtl-sdr = {
+    enable = lib.mkEnableOption ''
+      Enables rtl-sdr udev rules and ensures 'plugdev' group exists.
+      This is a prerequisite to using devices supported by rtl-sdr without
+      being root, since rtl-sdr USB descriptors will be owned by plugdev
+      through udev.
+    '';
+  };
+
+  config = lib.mkIf cfg.enable {
+    services.udev.packages = [ pkgs.rtl-sdr ];
+    users.groups.plugdev = {};
+  };
+}

nixos/modules/module-list.nix

@@ -59,6 +59,7 @@
   ./hardware/pcmcia.nix
   ./hardware/printers.nix
   ./hardware/raid/hpsa.nix
+  ./hardware/rtl-sdr.nix
   ./hardware/steam-hardware.nix
   ./hardware/system-76.nix
   ./hardware/tuxedo-keyboard.nix