Separating voice activity flag from audio level in RtpHeaderExtension.

VAD flag was embedded in RtpHeaderExtension.audioLevel, which is not easy to interpret. This CL tries to separate the flag with the actual audio level.

BUG=
R=andrew@webrtc.org, henrik.lundin@webrtc.org

Review URL: https://codereview.webrtc.org/1272343003 .

Cr-Commit-Position: refs/heads/master@{#9691}
5 files changed