Only include extra Wireguard module on old Kernels

... that don't have it by default. (<5.6)

morph/lib/vagrant-guest.nix

 # Minimal configuration that vagrant depends on
 
-{ config, pkgs, ... }:
+{ config, pkgs, lib, ... }:
 let
   # Vagrant uses an insecure shared private key by default, but we
   # don't use the authorizedKeys attribute under users because it should be
@@ -22,8 +22,10 @@ in
   # Enable the OpenSSH daemon.
   services.openssh.enable = true;
 
-  # Wireguard kernel module
-  boot.extraModulePackages = [ config.boot.kernelPackages.wireguard ];
+  # Wireguard kernel module for Kernels < 5.6
+  boot = lib.mkIf (lib.versionOlder pkgs.linuxPackages.kernel.version "5.6") {
+    extraModulePackages = [ config.boot.kernelPackages.wireguard ] ;
+  };
 
   # Enable DBus
   services.dbus.enable    = true;