uORB: remove lost message count per DeviceNode

- update 'uorb status' to print basic info for all advertised DeviceNodes
 - report vehicle_command gaps in commander, navigator, mavlink

src/modules/uORB/uORBDeviceNode.hpp

@@ -176,18 +176,16 @@ public:
 	int update_queue_size(unsigned int queue_size);
 
 	/**
-	 * Print statistics (nr of lost messages)
-	 * @param reset if true, reset statistics afterwards
-	 * @return true if printed something, false otherwise (if no lost messages)
+	 * Print statistics
+	 * @param max_topic_length max topic name length for printing
+	 * @return true if printed something, false otherwise
 	 */
-	bool print_statistics(bool reset);
+	bool print_statistics(int max_topic_length);
 
 	uint8_t get_queue_size() const { return _queue_size; }
 
 	int8_t subscriber_count() const { return _subscriber_count; }
 
-	uint32_t lost_message_count() const { return _lost_messages; }
-
 	unsigned published_message_count() const { return _generation.load(); }
 
 	const orb_metadata *get_meta() const { return _meta; }
@@ -239,7 +237,7 @@ private:
 	 * @return bool
 	 *   Returns true if the data was copied.
 	 */
-	bool copy_locked(void *dst, unsigned &generation);
+	bool copy_locked(void *dst, unsigned &generation) const;
 
 	struct UpdateIntervalData {
 		uint64_t last_update{0}; /**< time at which the last update was provided, used when update_interval is nonzero */
@@ -259,10 +257,6 @@ private:
 	px4::atomic<unsigned>  _generation{0};  /**< object generation count */
 	List<uORB::SubscriptionCallback *>	_callbacks;
 
-	// statistics
-	uint32_t _lost_messages = 0; /**< nr of lost messages for all subscribers. If two subscribers lose the same
-					message, it is counted as two. */
-
 	ORB_PRIO _priority;  /**< priority of the topic */
 	const uint8_t _instance; /**< orb multi instance identifier */
 	bool _advertised{false};  /**< has ever been advertised (not necessarily published data yet) */