Int 2F Fn B804  - Network - Set Network Event Post Handler                 [N]

   AX = B804h
   CX = (10NET) 0370h if 10Windows is hooking post handler
   ES:BX -> new event post handler

Notes: used in conjunction with AX=B803h to hook into the network event post
     routine
   this function is supported by 10NET v5.0
   The specified handler is called on any network event.  Two events are
     defined: message received and critical network error.

See Also: AX=B803h,AX=B904h

Values post routine is called with:
   AX = 0000h single block message
       DS:SI -> ASCIZ originator name
       DS:DI -> ASCIZ destination name
       ES:BX -> text header (see below)
   AX = 0001h start multiple message block
       CX = block group ID
       DS:SI -> ASCIZ originator name
       DS:DI -> ASCIZ destination name
   AX = 0002h multiple block text
       CX = block group ID
       ES:BX -> text header (see below)
   AX = 0003h end multiple block message
       CX = block group ID
   AX = 0004h message aborted due to error
       CX = block group ID
   AX = 0101h server received badly formatted network request

       Return: AX = FFFFh (PC LAN will process error)
   AX = 0102h unexpected network error
       ES:BX -> NCB (see INT 5C)
   AX = 0103h server received INT 24 error
       other registers as for INT 24, except AH is in BH

       Return: as below, but only 0000h and FFFFh allowed

Return: AX = response code
       0000h user post routine processed message
       0001h PC LAN will process message, but message window not displayed
       FFFFh PC LAN will process message

Format of text header:
Offset Size    Description
 00h   WORD    length of text (maximum 512 bytes)
 02h  N BYTEs  text of message

Note:  all CRLF sequences in message text are replaced by 14h