uORB::DeviceNode: reduce the size of some members

The limits the maximum queue size to 255, which I think is ok for the
forseable future.

sizeof(uORB::DeviceNode) is reduces from 128 to 112 on NuttX, and with
~80 instances, this saves over 1KB of RAM.

src/modules/uORB/uORBDevices.cpp

@@ -93,14 +93,11 @@ uORB::DeviceNode::DeviceNode(const struct orb_metadata *meta, const char *name,
 	_data(nullptr),
 	_last_update(0),
 	_generation(0),
-	_priority(priority),
+	_priority((uint8_t)priority),
 	_published(false),
 	_queue_size(queue_size),
-	_publisher(0),
-#ifdef __PX4_NUTTX
-	_IsRemoteSubscriberPresent(false),
-#endif
-	_subscriber_count(0)
+	_subscriber_count(0),
+	_publisher(0)
 {
 	// enable debug() calls
 	//_debug_enabled = true;
@@ -749,7 +746,8 @@ int uORB::DeviceNode::update_queue_size(unsigned int queue_size)
 		return PX4_OK;
 	}
 
-	if (_data || _queue_size > queue_size) {
+	//queue size is limited to 255 for the single reason that we use uint8 to store it
+	if (_data || _queue_size > queue_size || queue_size > 255) {
 		return ERROR;
 	}