INT 68 - APPC/PC - CHANGE LOGICAL UNIT
        AH = 03h subfn 2A00h
        DS:DX -> control block (see below)
Return: control block updated

Format of control block:
Offset  Size    Description
 00h 12 BYTEs   reserved
 0Ch    WORD    2A00h (verb "Change Logical Unit")
 0Eh  6 BYTEs   00h
 14h    DWORD   (big-endian) return code (see AH=01h/SF=1B00h)
 18h    WORD    00h
 1Ah  8 BYTEs   (big-endian) logical unit ID
 22h    DWORD   pointer to CREATE_TP_EXIT routine
                FFFFFFFFh reject incoming ALLOCATEs
                00000000h queue ALLOCATEs
 26h    DWORD   00000000h
 2Ah    DWORD   pointer to SYSTEM_LOG_EXIT routine, FFFFFFFFh= don't log errors
 2Eh    DWORD   00000000h
 32h    BYTE    maximum TPs
 33h    BYTE    00h stop QUEUE_ALLOCATEs
                01h resume QUEUE_ALLOCATEs
 34h    DWORD   pointer to LU_LU_PASSWORD_EXIT routine, FFFFFFFFh = no exit
 38h    DWORD   00000000h

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