orb: add optional queuing of messages

This adds two uORB API calls:
- orb_advertise_queue
- orb_advertise_multi_queue

Both add a queue_size parameter to define a maximum number of buffered
item. The existing orb calls use all a queue size of one and thus their
behavior is unchanged. If a writer publishes too fast, the oldest elements
from the queue are silently dropped.
The returned timestamp is always the one from the latest message in the
queue.

Queue size can be set via ioctl during advertisement phase. After that it
cannot be changed anymore.

src/modules/uORB/uORB.cpp

@@ -45,12 +45,23 @@ orb_advert_t orb_advertise(const struct orb_metadata *meta, const void *data)
 	return uORB::Manager::get_instance()->orb_advertise(meta, data);
 }
 
+orb_advert_t orb_advertise_queue(const struct orb_metadata *meta, const void *data, int queue_size)
+{
+	return uORB::Manager::get_instance()->orb_advertise(meta, data, queue_size);
+}
+
 orb_advert_t orb_advertise_multi(const struct orb_metadata *meta, const void *data, int *instance,
 				 int priority)
 {
 	return uORB::Manager::get_instance()->orb_advertise_multi(meta, data, instance, priority);
 }
 
+orb_advert_t orb_advertise_multi_queue(const struct orb_metadata *meta, const void *data, int *instance,
+				       int priority, int queue_size)
+{
+	return uORB::Manager::get_instance()->orb_advertise_multi(meta, data, instance, priority, queue_size);
+}
+
 int orb_unadvertise(orb_advert_t handle)
 {
 	return uORB::Manager::get_instance()->orb_unadvertise(handle);