Add non_ref_for_inter_layer_pred to VP9 RTP.

This converts the reserved bit in VP9 RTP payload descriptor into the
flag which indicates whether current frame can be used for prediction
of next spatial layer or not.

VP9 encoder wrapper sets non_ref_for_inter_layer_pred=false for all
frames for now.

Bug: none
Change-Id: I32f68868686475905fb09173cffd2b6e1bedcb7c
Reviewed-on: https://webrtc-review.googlesource.com/71080
Commit-Queue: Sergey Silkin <ssilkin@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23010}
diff --git a/modules/video_coding/include/video_codec_interface.h b/modules/video_coding/include/video_codec_interface.h
index 204098c..aad3759 100644
--- a/modules/video_coding/include/video_codec_interface.h
+++ b/modules/video_coding/include/video_codec_interface.h
@@ -48,6 +48,7 @@
                              // coded frame(s).
   bool flexible_mode;
   bool ss_data_available;
+  bool non_ref_for_inter_layer_pred;
 
   // TODO(nisse): Used on receive side only. Move elsewhere?
   int tl0_pic_idx;  // Negative value to skip tl0PicIdx.