成员的完整列表，这些成员属于 aiot_mqtt_upload_file_opt_t,包括所有继承而来的类成员

digest	aiot_mqtt_upload_file_opt_t
extra_params	aiot_mqtt_upload_file_opt_t
file_name	aiot_mqtt_upload_file_opt_t
file_size	aiot_mqtt_upload_file_opt_t
mode	aiot_mqtt_upload_file_opt_t
read_data_handler	aiot_mqtt_upload_file_opt_t
userdata	aiot_mqtt_upload_file_opt_t