Int 61 Fn 000F  - Banyan Vines - Close Socket                              [N]

   AX = 000Fh subfn 0004h
   CX:BX -> request block (see #3120)
   DX = application's data segment (should be = CX)
   ES = DS

Return: AX = status
       0000h successful
       00A5h resource not available
Desc:  Closes a socket identified by its socket handle

Format of request block:
Offset Size    Description (Table 3120)
 00h   WORD    0004h
 02h   WORD    magic number (FEFEh)
 04h   WORD    buffer for return code (set to 0 before calling)
 06h   WORD    reserved (will be set to client DS)
 08h   WORD    reserved (obviously not used; set to 0 before calling)
 0Ah   DWORD   far pointer to socket handle (2 bytes)
 0Eh   WORD    process handle (see AX=000Fh/SF=0008h)