as an alternative to NextPacket function to allow cleaner iterating over stacked rtcp packets. Bug: webrtc:5565 Change-Id: I261afe2684e5fcb5fa3e7bcce272fbefeebd0b66 Reviewed-on: https://webrtc-review.googlesource.com/21360 Reviewed-by: Niels Moller <nisse@webrtc.org> Commit-Queue: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20615}