INT 61 - Banyan VINES - "Soclose" - CLOSE A SOCKET
        AX = 0001h
        DS:DX -> communications control block (function 0004h)
Return: AX = status
            0000h  successful
            0001h  service not installed
            0002h  invalid service ID
            0003h-000Ah reserved for BANV interface errors
            0097h  invalid socket identifier
Note:   BANYAN can use any interrupt from 60h through 66h.  The Banyan
          interrupt handler is identified by the string "BANV" in the four
          bytes immediately preceding the interrupt handler

Format of control block:
Offset  Size    Description
 00h    WORD    0004h
 02h    WORD    pointer to argument block (see below)
 04h    WORD    error return code
 06h  4 BYTEs   reserved

Format of argument block:
Offset  Size    Description
 00h    WORD    socket identifier