To free up RtpVideoHeader::generic field for codec agnostic details from an rtp header extension. Bug: webrtc:10342 Change-Id: I7b9d869b2ecfedb96dfd860be47ed8dffa058749 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/166175 Commit-Queue: Danil Chapovalov <danilchap@webrtc.org> Reviewed-by: Niels Moller <nisse@webrtc.org> Reviewed-by: Philip Eliasson <philipel@webrtc.org> Cr-Commit-Position: refs/heads/master@{#30396}