INT 68 - APPC/PC - CHANGE NUMBER OF SESSIONS
        AH = 06h
        DS:DX -> control block (see below)
Return: control block updated

Format of control block:
Offset  Size    Description
 00h 12 BYTEs   reserved
 0Ch    WORD    1500h (verb "Change Number of Sessions")
 0Eh  6 BYTEs   00h
 14h    WORD    (big-endian) primary return code (see AH=02h)
 16h    DWORD   (big-endian) secondary return code (see below, AH=01h/SF=1B00h)
 1Ah  8 BYTEs   (big-endian) logical unit ID
 22h  8 BYTEs   blanks
 2Ah  8 BYTEs   (big-endian) partner logical unit name
 32h  8 BYTEs   (big-endian) mode name
 3Ah    BYTE    bit 7: use MODE_NAME_SELECT_ALL rather than MODE_NAME
                bit 6: set negotiable values
 3Bh    BYTE    partner logical unit mode session limit
 3Ch    BYTE    minimum CONWINNERS_SOURCE
 3Dh    BYTE    maximum CONWINNERS_TARGET
 3Eh    BYTE    automatic activation
 3Fh    BYTE    00h
 40h    BYTE    bit 7: drain target
                bit 6: drain source
                bit 5: target responsible, not source

Values for secondary return code (see also AH=01h/SF=1B00h):
 0000h  accepted
 0001h  negotiated
 0003h  bad logical unit ID
 0004h  allocation failure, no retry
 0005h  allocation failure, retry
 0151h  can't raise limits
 0153h  all modes must reset
 0154h  bad SNASVCMG limits
 0155h  minimum greater than total
 0156h  mode closed (primary return code = 1)
        CNOS mode closed (primary return code = 18h)
 0157h  bad mode name (primary return code = 1)
        CNOS bad mode name (primary return code = 18h)
 0159h  reset SNA drains
 015Ah  single not SRC response
 015Bh  bad partner logical unit
 015Ch  exceeds maximum allowed
 015Dh  change SRC drains
 015Eh  logical unit detached
 015Fh  CNOS command race reject

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