If resubscribe, replace the message handler with new user callback
If resubscribe, replace the message handler with new user callback

Signed-off-by: miketran78727 <7744469cb218816982a3e45f9177ac9f8608ed96@us.ibm.com>

eclipse/paho.mqtt.embedded-c,eclipse/paho.mqtt.embedded-c,eclipse/paho.mqtt.embedded-c,eclipse/paho.mqtt.embedded-c,monstrenyatko/ArduinoMqtt,monstrenyatko/ArduinoMqtt,eclipse/paho.mqtt.embedded-c