Function esp_mqtt_client_unsubscribe

pub unsafe extern "C" fn esp_mqtt_client_unsubscribe(
    client: *mut esp_mqtt_client,
    topic: *const u8,
) -> i32

@brief Unsubscribe the client from defined topic

Notes:

• Client must be connected to send unsubscribe message
• It is thread safe, please refer to esp_mqtt_client_subscribe_single for details

@param client MQTT client handle @param topic

@return message_id of the subscribe message on success -1 on failure