Int 21 Fn FF9F  - Topware Network Os V5.10+ - Enable/disable Topterm Serv  [N]

   AX = FF9Fh
   CL = new state (00h disable [disregard TopTerm packets], 01h enable)

Return: AL = status (00h successful, FFh failed)

Note:  this function is only supported by Workstations, not the server