Inline default constructors for MediaChannel structs
Inline default constructors for MediaChannel structs

Bug: None
Change-Id: I72b534c49d3f26e988d1c92aae09435a9483a930
Reviewed-on: https://webrtc-review.googlesource.com/37143
Commit-Queue: Steve Anton <93f73658da16553b94c040887a439a155812e54e@webrtc.org>
Reviewed-by: Peter Thatcher <86dc5d06abaeadbc7f61dd701fafcbca29ff9bbc@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#21540}
ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc