unsigned char *silc_argument_get_arg_type(SilcArgumentPayload payload,
                                              SilcUInt32 type,
                                              SilcUInt32 *ret_len);

    Returns argument by type. The returned argument has type `type'
    in the Argument Payload. Each argument has their own type (or zero
    if no specific type is set). The length of the argument is returned
    to the `ret_len'. The caller must not free the returned argument.
    Returns NULL on error.