Fixed issue with wrong timestamp

Telemetry service used steady_clock for generating timestamps, but it
produced incorrect time. This change makes telemetry service use
steady_clock for intervals and system_clock for timestamps.

Changed readings timestamp to display current timestamp instead of a
time when reading was received.

Tested:
- correct timestamp is visible on dbus
- other telemetry service features are still working

Change-Id: Ic49f45640532cfffaeff5e0bd5591e6d99e5def5
Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
diff --git a/src/sensor.hpp b/src/sensor.hpp
index 3c9c746..d2c3ec2 100644
--- a/src/sensor.hpp
+++ b/src/sensor.hpp
@@ -2,7 +2,7 @@
 
 #include "interfaces/sensor.hpp"
 #include "interfaces/sensor_listener.hpp"
-#include "types/milliseconds.hpp"
+#include "types/duration_types.hpp"
 #include "utils/unique_call.hpp"
 
 #include <boost/asio/high_resolution_timer.hpp>
@@ -53,7 +53,7 @@
 
     utils::UniqueCall uniqueCall;
     std::vector<std::weak_ptr<interfaces::SensorListener>> listeners;
-    uint64_t timestamp = 0;
+    Milliseconds timestamp = Milliseconds{0u};
     std::optional<double> value;
     std::unique_ptr<sdbusplus::bus::match_t> signalMonitor;
 };