mavlink_stream: update fd list after changing interval

The fd list was no longer in sync -> a stale descriptor was used for
polling -> causes memory leak

src/modules/mavlink/mavlink_stream.cpp

@@ -340,6 +340,13 @@ MavlinkStreamPoll::set_interval(uint16_t stream_id, int interval_ms)
 		}
 	}
 
+	// Update fds
+	for (int j = 0; j < _count; j++) {
+		_fds[j].fd = _orbs[j].fd;
+		_fds[j].events = POLLIN;
+		_fds[j].revents = 0;
+	}
+
 	pthread_mutex_unlock(&_mtx);
 	return PX4_OK;
 }