If the connection to the MQTT broker drops, e.g. because the broker is offline for a while, the firmware did never try to reconnect. This PR implements a reconnect functionality. If the function mqtt_send_value() detects no connection, mqtt_connect() will be called and the next mqtt_send_value() will be able to post successfully again.
If the connection to the MQTT broker drops, e.g. because the broker is offline for a while, the firmware did never try to reconnect. This PR implements a reconnect functionality. If the function mqtt_send_value() detects no connection, mqtt_connect() will be called and the next mqtt_send_value() will be able to post successfully again.