core: build keyfile plugin into NetworkManager

Since settings storage is now handled by NetworkManager, we must
have the ability to read/write all connection types at all times.
Since the 'keyfile' plugin is the only plugin that can handle all
connection types, build it into NetworkManager.

system-settings/plugins/keyfile/plugin.c

@@ -662,8 +662,8 @@ system_config_interface_init (NMSystemConfigInterface *system_config_interface_c
 	system_config_interface_class->get_unmanaged_specs = get_unmanaged_specs;
 }
 
-G_MODULE_EXPORT GObject *
-nm_system_config_factory (void)
+GObject *
+nm_settings_keyfile_plugin_new (void)
 {
 	static SCPluginKeyfile *singleton = NULL;