Add accessors to the types in the RTPVideoTypeHeader in RTPVideoHeader.

This CL is in preparation to change the RTPVideoTypeHeader into an absl::variant.

Bug: none
Change-Id: I1672d866df0395f3417d8e278cc67f017ab0ff98
Reviewed-on: https://webrtc-review.googlesource.com/87261
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23856}
diff --git a/modules/video_coding/packet_buffer.cc b/modules/video_coding/packet_buffer.cc
index 8960b1c..28ade46 100644
--- a/modules/video_coding/packet_buffer.cc
+++ b/modules/video_coding/packet_buffer.cc
@@ -304,7 +304,7 @@
 
         if (is_h264 && !is_h264_keyframe) {
           const RTPVideoHeaderH264& header =
-              data_buffer_[start_index].video_header.codecHeader.H264;
+              data_buffer_[start_index].video_header.h264();
 
           if (header.nalus_length >= kMaxNalusPerPacket)
             return found_frames;