acnet_callback_init

	status.i4.v = acnet_callback_init(typecode.i4.v, tc_handler.f.v, 
					  user_arg.g.v, ast_flag.l4.v)

	This routine registers a typecode with the ACNET Request Callback
	Facility.  The ACNET Request Callback Facility will call the
	"tc_handler" function whenever an ACNET message for "typecode" is
	received.  The handler function is responsible for constructing and
	sending any reply.  Requests (as opposed to USM's) must be either
	replied to or canceled.  A request sent to an ACNET callback handler
	must contain at a minimum a two byte integer containing the
	value, "typecode".  This routes the request to the proper handler.

	typecode	typecode assigned to the application or UTI
			(constants are in 'acnet')
	tc_handler	Typecode handler function which is called back when
			a request or USM is received for "typecode". It has
			the following prototype:
			void tc_handler(uab_request_t *uab, void *user_arg)
	user_arg	This argument is passed back to the handler callback
			function.
	ast_flag	If TRUE, the handler function will be called at AST
			level.  Otherwise, it will be called later at NON-AST 
			level.

	This function returns ACNET status values as follows:

	OK			success
	CLIB_INVARG		invalid type code passed
	CLIB_NOINIT		acnet_callback_handle never called

	This function requires the following include files:

	cnsparam_h, acnet_h, clib_h, acnet_errors_h

	Related functions:

	acnet_callback_handle, acnet_callback_flush,
	acnet_callback_handle_return

	C/C++ usage:

	int	status;
	int	typecode = ACNET_CALLBACK_DIO;
	int	ast_flag = FALSE;
	void	tc_handler(uab_request_t *uab, void *user_arg);
	void	*user_arg = (void *) NULL;

	status = acnet_callback_init(typecode,tc_handler,user_arg,ast_flag);