Implement H.264 packetization mode 0.

This approach extends the H.264 specific information with
a packetization mode enum.

Status: Parameter is in code. No way to set it yet.

Rebase of CL  2009213002

BUG=600254

Review-Url: https://codereview.webrtc.org/2337453002
Cr-Commit-Position: refs/heads/master@{#15032}

webrtc/modules/video_coding/codec_database.cc

@@ -64,6 +64,7 @@ VideoCodecH264 VideoEncoder::GetDefaultH264Settings() {
 
   h264_settings.frameDroppingOn = true;
   h264_settings.keyFrameInterval = 3000;
+  h264_settings.packetization_mode = kH264PacketizationMode1;
   h264_settings.spsData = nullptr;
   h264_settings.spsLen = 0;
   h264_settings.ppsData = nullptr;