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

nixos/modules/module-list.nix

@@ -344,6 +344,7 @@
   ./services/networking/tlsdated.nix
   ./services/networking/tox-bootstrapd.nix
   ./services/networking/tvheadend.nix
+  ./services/networking/ubuntu-fan.nix
   ./services/networking/unbound.nix
   ./services/networking/unifi.nix
   ./services/networking/vsftpd.nix

nixos/modules/services/networking/ubuntu-fan.nix

@@ -0,0 +1,60 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.networking.ubuntu-fan;
+  modprobe = "${config.system.sbin.modprobe}/sbin/modprobe";
+
+in
+
+{
+
+  ###### interface
+
+  options = {
+
+    networking.ubuntu-fan = {
+
+      enable = mkEnableOption "Ubuntu FAN Networking";
+
+    };
+
+  };
+
+
+  ###### implementation
+
+  config = mkIf cfg.enable {
+
+    environment.systemPackages = [ pkgs.fanctl ];
+
+    systemd.services.ubuntu-fan = {
+      description = "Ubuntu FAN Networking";
+      wantedBy = [ "multi-user.target" ];
+      after = [ "network-online.target" ];
+      before = [ "docker.service" ];
+      restartIfChanged = false;
+      preStart = ''
+        if [ ! -f /proc/sys/net/fan/version ]; then
+          ${modprobe} ipip
+          if [ ! -f /proc/sys/net/fan/version ]; then
+            echo "The Ubuntu Fan Networking patches have not been applied to this kernel!" 1>&2
+            exit 1
+          fi
+        fi
+
+        mkdir -p /var/lib/ubuntu-fan
+      '';
+      serviceConfig = {
+        Type = "oneshot";
+        RemainAfterExit = true;
+        ExecStart = "${pkgs.fanctl}/bin/fanctl up -a";
+        ExecStop = "${pkgs.fanctl}/bin/fanctl down -a";
+      };
+    };
+
+  };
+
+}