Format of FaxBIOS SYS_LOGOUT command buffer:
Offset	Size	Description	)
 00h	WORD	structure size
 02h	WORD	function number
 04h	WORD	return code
 06h	WORD	client ID
 08h	DWORD	client tag (for client's internal use)
 0Ch  6 BYTEs	future expansion
 12h	WORD	structure size