Prior to this change, if the clock thread is disabled, then
disconnecting and reconnecting the X52 device would cause the daemon to
not detect the transition. As a result, the daemon would stay in a state
where it thinks the device is still connected, and therefore, not
actually apply any of the saved configuration, until it received a
SIGHUP to refresh the configuration.
This change adds a routine that sends a dummy vendor command. This
vendor command does nothing on my X52 Pro (VID 06a3, PID 0762), but
serves as a check to see if the daemon can send vendor commands to the
device. If the device is indeed disconnected, then that is a sufficient
indicator to disable the update thread and re-enable the acquisition
thread.
nirenjan