Make video_codec_interface visible.
Make video_codec_interface visible.

These headers contain public defines for the module, so it makes
sense it's visible.

Bug: webrtc:7620
Change-Id: I4c2604dcfb3beb4bfa0803a15d0e1a89c374e4cf
Reviewed-on: https://webrtc-review.googlesource.com/39261
Commit-Queue: Patrik Höglund <b486136ee68458b09c92c86c39f451c87d6ef6a1@webrtc.org>
Reviewed-by: Mirko Bonadei <d2c43c210eae6feef04f53bae50885e8152edcca@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#21616}
TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc