Optimize filtering

[DmitryAstafyev]

Configuration of filters is declared here:

pub struct DltFilterConfig {
    /// only select log entries with level MIN_LEVEL and more severe
    ///
    /// ``` text
    ///  1 => FATAL
    ///  2 => ERROR
    ///  3 => WARN
    ///  4 => INFO
    ///  5 => DEBUG
    ///  6 => VERBOSE
    /// ```
    pub min_log_level: Option<u8>,
    /// what app ids should be allowed.
    pub app_ids: Option<Vec<String>>,
    /// what ecu ids should be allowed
    pub ecu_ids: Option<Vec<String>>,
    /// what context ids should be allowed
    pub context_ids: Option<Vec<String>>,
    /// how many app ids exist in total
    pub app_id_count: i64,
    /// how many context ids exist in total
    pub context_id_count: i64,
}

But the usage of fields app_id_count and context_id_count isn't clean. Probably it make sense to get rid of this?