INT 21 - PC/TCP IPCUST.SYS - READ CONFIGURATION DATA
        AH = 3Fh
        BX = handle for character device "$IPCUST"
        CX = number of bytes to read
        DS:DX -> buffer for configuration data (see below)
Return: CF clear if successful
            AX = number of bytes actually read
        CF set on error
            AX = error code (05h,06h) (see AH=59h)
Notes:  if less than the entire data is read or written, the next read/write
          continues where the previous one ended; IOCTL calls AX=4402h and
          AX=4403h both reset the location at which the next operation starts
          to zero
        the data pointer is also reset to zero if the previous read or write
          reached or exceeded the end of the data, when the current function
          is read and the previous was write, or vice versa
SeeAlso: AX=4402h"IPCUST"

Format of configuration data:
Offset  Size    Description
 00h 12 BYTEs   IPCUST.SYS device driver header
 12h    BYTE    ???
 13h    BYTE    ???
 14h    WORD    ???
 16h    BYTE    bit flags
                bit 0: send BS rather than DEL for BackSpace key
                bit 1: wrap long lines
 17h    BYTE    ???
 18h 64 BYTEs   ASCIZ hostname
 58h 64 BYTEs   ASCIZ domain name
                (fully qualified domain name is hostname.domain-name)
 98h 16 BYTEs   ASCIZ username
 A8h 64 BYTEs   ASCIZ full name
 E8h 64 BYTEs   ASCIZ office address
128h 32 BYTEs   ASCIZ phone number
148h    WORD    offset from GMT in minutes
14Ah  4 BYTEs   ASCIZ timezone name
14Eh    WORD    number of time servers
150h  ? DWORDs  IP addresses for time servers (big-endian)
        ???
164h    WORD    number of old-style name servers
166h  3 DWORDs  IP addresses for name servers (big-endian)
172h    WORD    number of domain name servers
174h  3 DWORDs  IP addresses for domain name servers (big-endian)
180h    DWORD   IP address of default gateway (big-endian)
184h    DWORD   IP address of log server (big-endian)
188h    DWORD   IP address of cookie server (big-endian)
18Ch    DWORD   IP address of lpr server (big-endian)
190h    DWORD   IP address of imagen print server
194h 54 BYTEs   ???
1E8h    WORD    TCP default window size in bytes
1EAh    WORD    TCP low window size
1ECh 64 BYTEs   ASCIZ host tabel filename
22Ch  2 BYTEs   ???
22Eh 80 BYTEs   ASCIZ mail relay host name
27Eh    BYTE    ???
27Fh    BYTE    ??? bit flags
280h 44 BYTEs   ???
2ACh    WORD    ???
2AEh 202 BYTEs  ???