Int 21 Fn 5FE1  - LANtastic - Set DOS Service Vector                       [N]

   AX = 5FE1h
   ES:BX -> FAR routine to call when DOS services are available

Return: CF clear if successful
   CF set on error
       AX = error code

Note:  new handler must chain to previous handler as its first action

See Also: AX=5FE0h