INT 61 - Banyan VINES - INTERCEPT VINES 25th-LINE MESSAGES AT LOCAL PC
        AX = 0008h
        BX = 0003h
        DS:DX -> request block
Return: AX = status
            0000h successful
            0001h network software not installed or incompatible
Notes:  message handler should not call BIOS or DOS functions, and should
          either call next handler or simply return
        to stop intercepting messages, set prev and next request blocks to
          point at each other
SeeAlso: AX=0008h/BX=0002h

Format of request block:
Offset  Size    Description
 00h    DWORD   pointer to user-written message handler
 04h    DWORD   pointer to next request block (filled in by VINES)
 08h    DWORD   pointer to previous request block (filled in by VINES)
 0Ch    DWORD   pointer to message storage area (filled by VINES) (see below)

Format of message storage area:
Offset  Size    Description
 00h 16 BYTEs   IPC port of message sender (see AX=0001h#"Sosock")
 10h    BYTE    message flags
 11h    WORD    reserved
 13h    BYTE    length of message
 14h 80 BYTEs   message text

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