wsl-distro: introduce wsl.kernelModules option

WSL now supports kernel modules and come with a bunch configured as `m`
and can be loaded this way. For example `vhci-hcd` used by usbip has
changed from `y` to `m` and hence need to be explicitly loaded.

Author: terlar

modules/wsl-distro.nix

@@ -10,6 +10,14 @@ in
   options.wsl = with types; {
     enable = mkEnableOption "support for running NixOS as a WSL distribution";
     useWindowsDriver = mkEnableOption "OpenGL driver from the Windows host";
+    kernelModules = mkOption {
+      type = listOf str;
+      default = [ ];
+      description = ''
+        The set of kernel modules to be loaded in the second stage of
+        the boot process via systemd-modules-load.service.
+      '';
+    };
     binShPkg = mkOption {
       type = package;
       internal = true;
@@ -109,6 +117,9 @@ in
         (mkIf config.wsl.wslConf.network.generateResolvConf {
           "resolv.conf".enable = false;
         })
+        (mkIf cfg.kernelModules != [] {
+          "modules-load.d/nixos.conf".text = concatStringsSep "\n" cfg.kernelModules;
+        })
       ];
     };