nixos/modprobe: replace boot.isContainer with boot.modprobeConfig.enable

nixos/modules/system/boot/modprobe.nix

···
   ###### interface
 
   options = {
+    boot.modprobeConfig.enable = mkEnableOption (lib.mdDoc "modprobe config. This is useful for systemds like containers which do not require a kernel.") // {
+      default = true;
+    };
 
     boot.blacklistedKernelModules = mkOption {
       type = types.listOf types.str;
···
 
   ###### implementation
 
-  config = mkIf (!config.boot.isContainer) {
+  config = mkIf config.boot.modprobeConfig.enable {
 
     environment.etc."modprobe.d/ubuntu.conf".source = "${pkgs.kmod-blacklist-ubuntu}/modprobe.conf";
 

nixos/modules/virtualisation/container-config.nix

···
 
     # Disable some features that are not useful in a container.
 
+    # containers don't have a kernel
     boot.kernel.enable = false;
+    boot.modprobeConfig.enable = false;
 
     console.enable = mkDefault false;