nixos/powertop: wait for hardware to initialize

We should wait until after `multi-user.target` is triggered to allow
hardware to finish initializing, such as network devices and USB drives.
This ensures `powertop --auto-tune` sets more tunables to "Good".

Fixes #66820

nixos/modules/tasks/powertop.nix

@@ -15,6 +15,7 @@ in {
     systemd.services = {
       powertop = {
         wantedBy = [ "multi-user.target" ];
+        after = [ "multi-user.target" ];
         description = "Powertop tunings";
         path = [ pkgs.kmod ];
         serviceConfig = {