The function for automatically updating the image from the master to
a device that is attempting to join the stack.
When a new device tries to join a stack, STM verifies the image
consistency between the joining device and the master.
If the joining device uses a different image version than the master,
the function updates the joining device with the image of the master.
When this function is disabled, the new device can not join the stack
if it uses a different software version than the master.
disabled: disable auto update function
enabled: enable auto update function