The value of tmnxSubAuthPlcyFallbackUserDb specifies the local user
database to use for authentication while no RADIUS server is availabe.
This object is only relevant while the value of the object
'tmnxSubAuthPlcyFallbackAction' is equal to 'userDb'.
The value of this object must be set together with the value of
the object tmnxSubAuthPlcyFallbackAction.