utility_acb_register_function

	status.i4.v = utility_acb_register_function(callback_func.f.v,
						    callback_data.g.v)

	This routine registers a functiom to be called whenever a utility
	ACNET callback request is received by the calling program.

	callback_func	function which is called when a remote
			message is received to be called as follows:
			status.i4.v = callback_func(request.s.r,
						    callback_data.g.v,
						    reply.s.r,
						    reply_length.i4.r)
			("request" is a structure of type UTIL_ACB_REQUEST,
			 "callback_data" is a pointer to user-supplied data,
			 "reply" is a structure of type UTIL_ACB_REPLY,
			 "reply_length" is the returned reply length)
			(a value of NULL can be passed for this argument
			 to enable default behavior)
	callback_data	pointer to user-supplied data to be passed to
			the callback function (default is NULL)

	This function returns ACNET status values as follows:

	OK			success
	CLIB_DUPREQ		requested function is already registered

	This function requires the following include files:

	cnsparam_h, acnet_callbacks_h, acnet_errors_h

	Related functions:

	utility_acb_unregister_function, utility_acb_send_terminate_request,
	acnet_callback_init

	C/C++ usage:

	int	status;
	util_acb_function	callback_func;
	void	*callback_data = (void *) NULL;

	status = utility_acb_register_function(callback_func,callback_data);