System Default for frxMgtT392 - used when the
Download Configuration pushbutton on the channel unit
faceplate is pushed and when frxDefaultEnable is set to 1.
This controls how long (in seconds) the channel unit
will wait for a subscriber to send it an Annex-D poll
before declaring a link error from the subscriber.
This is the Annex-D T392 parameter (Typical value 15)