Int 7F Fn 15  - Alloy Ntnx, Mw386 - Get Next Full Channel                  [N]

   AH = 15h
   CL = 01h
   DX:DI -> full-channel structure

Return: AL = status
       00h successful
       01h busy
       0Ah no datagrams available

Note:  MW386 v1.0 returns the lowest channel with a datagram; newer versions
     and NTNX return the oldest datagram

See Also: AH=15h/CL=00h

Format of full-channel structure:
Offset Size    Description
 00h   BYTE    number of channel with oldest datagram
 01h   BYTE    sender ID