audio_coding: rename interface -> include

BUG=webrtc:5095
R=henrik.lundin@webrtc.org
TBR=tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1417173004 .

Cr-Original-Commit-Position: refs/heads/master@{#10444}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 74640895fafbb90a6630a6a91b80da0a7cff229c
117 files changed