fix(falco_metrics): make duration_sec a count and not a timestamp

The output will thus be a total which is what this metrics is.

Signed-off-by: Samuel Gaist <samuel.gaist@idiap.ch>

userspace/falco/falco_metrics.cpp

@@ -117,7 +117,7 @@ std::string falco_metrics::to_text(const falco::app::state& state)
 		static_metrics.push_back(libs_metrics_collector.new_metric("duration_sec",
 																	METRICS_V2_MISC,
 																	METRIC_VALUE_TYPE_U64,
-																	METRIC_VALUE_UNIT_TIME_TIMESTAMP_NS,
+																	METRIC_VALUE_UNIT_TIME_S_COUNT,
 																	METRIC_VALUE_METRIC_TYPE_NON_MONOTONIC_CURRENT,
 																	(uint64_t)((now - agent_info->start_ts_epoch) / ONE_SECOND_IN_NS)));