Broadcast messages (INT 21h, E1h - Novell NetWare 4.0)

        Entry:
          AH = E1h
          DS:SI -> request buffer
          ES:DI -> reply buffer
          Subfunction in third byte of request buffer
            00h  Send broadcast message
            01h  Get broadcase message
            02h  Disable station broadcasts
            03h  Enable station broadcasts
            04h  Send personal message
            05h  Get personal message
            06h  Open message pipe
            07h  Close message pipe
            08h  Check pipe status
            09h  Broadcast to console
        Return:
          AL = error code