mqtt: reconnect callback does not need to hang up
mqtt: reconnect callback does not need to hang up

The network stack has certainly done that for us at this point.
Similarly, since we're about to call mqtt_socket_disconnected, don't
bother unregistering the timer here, either.

nwf/nodemcu-firmware,nwf/nodemcu-firmware,nwf/nodemcu-firmware,nwf/nodemcu-firmware,nwf/nodemcu-firmware