connection_lost is always called after keep_alive_interval timeout even if network already restored

[JohnChain]

Here is my test step:

1. using async_client
2. set callback (connected and connection_lost)
3. set keep_alive_interval to 30s
4. set automatic_reconnect(1s, 32s)
5. run program and connected to mqtt server
6. disable network (eg: plugout cable)，and wait for 10s
7. enable network (eg: plugin cable) ，and the OS system network is restored within 10s

the connected callback is not call immediately, and the connection_lost callback called after timeout of keep_alive_interval(may be 1.5*30s).
I add reconnect in connection_lost, and after calling reconnect, the connected callback is called with message "automatic reconnect"

class callback : public virtual mqtt::callback{
public:
    void connected(const string& msg) {
        if(msg.compare("automatic reconnect") == 0){
            client->subscribe(sub_ctrl, QOS);
            client->subscribe(sub_result, QOS);
        }
        LOG_D("*** Connection created (%s) isconnencted:%d ***", msg.c_str(), client->is_connected());

    }
    void connection_lost(const std::string& msg) override {
        LOG_E("*** Connection Lost (%s), will reconnect ***", msg.c_str());
        client->reconnect();
    }

    void delivery_complete(mqtt::delivery_token_ptr tok) override {
        // LOG_D("[%ld]Delivery complete: %d", newtimeus, (tok ? tok->get_message_id() : -1));
    }

    void message_arrived(mqtt::const_message_ptr msg) {
	const std::string &sub_msg = msg->get_payload_str();
	// dispatch msg
    }
private:
};

int prepareMqttClient(mqtt::async_client &client, callback &cb, const char* username, const char* passwd){
    client->set_callback(cb);
    // Build the connect options, including SSL and a LWT message.
    auto sslopts = mqtt::ssl_options_builder()
                        .trust_store(strlen(cert_path)? cert_path:TRUST_STORE)
                        //.key_store(KEY_STORE)  /* enabled when Mutual Authentication*/
                        .error_handler([](const std::string& msg) {
                            LOG_E("SSL Error: %s", msg.c_str());
                        })
                        .finalize();


    auto willmsg = mqtt::message(LWT_TOPIC, LWT_PAYLOAD, QOS, true);
    auto connopts = mqtt::connect_options_builder()
                        .clean_session(true)
                        .connect_timeout(std::chrono::seconds(10))
                        .keep_alive_interval(std::chrono::seconds(30))
                        .max_inflight(1024)
                        .automatic_reconnect(std::chrono::seconds(1), std::chrono::seconds(32))
                        .user_name(username)
                        .password(passwd)
                        .will(std::move(willmsg))
                        .ssl(std::move(sslopts))
                        .finalize();
    // connect
}