nixos: add support for Ubuntu Fan Networking

This provides support for Ubuntu Fan Networking [1].

This includes:

* The fanctl package, and a corresponding NixOS service.
* iproute patches.
* kernel patches.

closes #9188

1: https://wiki.ubuntu.com/FanNetworking

pkgs/os-specific/linux/iproute/default.nix

@@ -1,4 +1,6 @@
-{ fetchurl, stdenv, flex, bison, db, iptables, pkgconfig }:
+{ fetchurl, stdenv, lib, flex, bison, db, iptables, pkgconfig
+, enableFan ? false
+}:
 
 stdenv.mkDerivation rec {
   name = "iproute2-4.1.1";
@@ -8,6 +10,8 @@ stdenv.mkDerivation rec {
     sha256 = "0vz6m2k6hdrjlg4x0r3cd75lg9ysmndbsp35pm8494zvksc7l1vk";
   };
 
+  patches = lib.optionals enableFan [ ./ubuntu-fan.patch ];
+
   preConfigure = ''
     patchShebangs ./configure
     sed -e '/ARPDDIR/d' -i Makefile