Update header formatters to FlexFEC draft 03.

The only difference is that the F and R bits have changed place.

BUG=webrtc:5654

Review-Url: https://codereview.webrtc.org/2495253002
Cr-Original-Commit-Position: refs/heads/master@{#15064}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 25b57ce08ec50afba780c9ae2c560248665a140f
3 files changed