INT 7F - Alloy NTNX, MW386 - SEND DATAGRAM
        AH = 11h
        DX:SI -> request block (see below)
Return: AL = status
            00h successful
            01h busy
            02h channel range error (not 00h-3Fh)
            03h invalid subfunction
            0Ah packet too large (or <2 bytes if NTNX)
            0Bh can't send packet to itself
            0Ch invalid number of destinations
            0Dh destination channel number out of range
            0Eh destination user is busy
            0Fh destination user has locked channel
            10h channel not open
            11h no datagram server on destination (NTNX)
Note:   if wildcard channel FFh used, actual channel number will be filled in

Format of request block:
Offset  Size    Description
 00h    DWORD   pointer to packet to send
 04h    WORD    packet size in bytes (1-4096)
 06h    BYTE    number of destinations for packet (max 1Fh)
 07h 31 BYTEs   destination user IDs (FFh = broadcast to all except sender)
 26h 31 BYTEs   destination channels (FFh = first available channel)
 45h 31 BYTEs   return destination statuses