Make VCMDecodeErrorMode optional when calling VideoCodingModule::SetReceiverRobustnessMode
Make VCMDecodeErrorMode optional when calling VideoCodingModule::SetReceiverRobustnessMode

This is a preparation for deleting other modes than
VCMDecodeErrorMode::kNoErrors.

Bug: webrtc:8064
Change-Id: I614f8012f306c5d59e72bdb851b582c286cdd130
Reviewed-on: https://webrtc-review.googlesource.com/c/116781
Reviewed-by: Erik Språng <3ab8c90c99d6dd7822e0fad803ab0211dd287ae5@webrtc.org>
Commit-Queue: Niels Moller <0057859e47d61d90529d0f66d9ef692cefedb46a@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#26195}
TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc