Tune NIC offloads for Tailscale exit node

modules/services/tailscale.nix

@@ -1,4 +1,4 @@
-{ ... }:
+{ pkgs, ... }:
 {
   services.tailscale.enable = true;
   services.tailscale.port = 41641;
@@ -8,4 +8,19 @@
     "--advertise-exit-node"
     "--hostname=bucur"
   ];
+
+  environment.systemPackages = [ pkgs.ethtool ];
+
+  systemd.services.tailscale-offload-tune = {
+    description = "Disable GRO forwarding for Tailscale exit node performance";
+    after = [ "network-online.target" ];
+    wants = [ "network-online.target" ];
+    serviceConfig = {
+      Type = "oneshot";
+      ExecStart = ''
+        /bin/sh -c '${pkgs.iproute2}/bin/ip -o route get 8.8.8.8 | ${pkgs.coreutils}/bin/cut -f 5 -d " " | xargs -r ${pkgs.ethtool}/bin/ethtool -K rx-udp-gro-forwarding on rx-gro-list off'
+      '';
+    };
+    wantedBy = [ "multi-user.target" ];
+  };
 }