tailscale: add exit node functionality to Gutterman

modules/nixos/services/tailscale/exit-node/client.nix

@@ -0,0 +1,8 @@
+{ config, ... }:
+
+{
+  services.tailscale = {
+    useRoutingFeatures = "client";
+    extraUpFlags = [ "--exit-node-allow-lan-access=true" ];
+  };
+}

modules/nixos/services/tailscale/exit-node/server.nix

@@ -0,0 +1,20 @@
+{ config, lib, pkgs, ... }:
+
+{
+  services.tailscale = {
+    useRoutingFeatures = "server";
+    extraUpFlags = [ "--advertise-exit-node" ];
+  };
+
+  # performance improvement
+  environment.systemPackages = [ pkgs.ethtool ];
+  services.networkd-dispatcher = {
+    enable = true;
+    rules."50-tailscale" = {
+      onState = [ "routable" ];
+      script = ''
+        ${lib.getExe pkgs.ethtool} -K eth0 rx-udp-gro-forwarding on rx-gro-list off
+      '';
+    };
+  };
+}