mqtt_client::will

Assign a will Message.

mqtt_client & will(
    will will
);

The will Message that the Broker should publish after the Network Connection is closed and it is not closed normally.

	Important
	This function takes action when the client is in a non-operational state, meaning the `mqtt_client::async_run` function has not been invoked. Furthermore, you can use this function after the `mqtt_client::cancel` function has been called, before the `mqtt_client::async_run` function is invoked again.