INT 69 - DECnet DOS 2.1+ - DATA LINK LAYER
        AH = 0Ah
        AL = function
            00h initialize
            01h open portal
            02h close portal
            03h enable multicast address
            04h disable multicast address
            05h transmit
            06h request transmit buffer
            07h deallocate transmit buffer
            08h read channel status
            09h read datalink portal list
            0Ah read information about a datalink portal
            0Bh read and/or clear counters
            0Ch request to boot from a network server
            0Dh enable Ethernet channel
            0Eh disable Ethernet channel
            0Fh start MOP/send a System ID message
            10h stop MOP
            11h get DECPARM
            12h set DECPARM
            13h external loopback
        ES:BX -> Datalink Communication Block
Return: AX = status
            00h successful
            01h hardware failed to initialize
            02h channel state was not off (must be off to execute that command)
            03h channel state is off (must be on to execute that command)
            04h address not set
            05h hardware missing
            06h buffer too small
            07h no more buffers available
            08h no more resources available
            09h promiscuous receiver active
            0Ah non exclusive
            0Bh unrecognized portal
            0Ch protocol type in use
            0Dh not a valid Multicast address
            0Eh outstanding calls
            0Fh hardware doesn't support receiving bad frames
            10h none outstanding
            11h no events
            12h broken
            13h buffer quota exceeded
            14h already initialized
            15h loopback failure

Format of Datalink Communication Block
Offset  Type    Description
 00h    WORD    portal ID
 02h  6 BYTEs   source address
 08h  6 BYTEs   destination address
 0Eh    DWORD   buffer pointer
 12h    WORD    buffer length
 14h    WORD    operation
 16h    BYTE    pad flag (used on open)
                    00h no pad
                    01h pad
 17h    BYTE    mode flag (used on open)
                    00h 802.3
                    01h Ethernet
                    02h promiscuous
 18h    DWORD   line status change function
 1Ch    DWORD   received data function
 20h    DWORD   transmitted data function
 24h    BYTE    maximum outstanding transmits/receives
 25h  2 BYTEs   protocol type
 27h    WORD    buffers lost