v4l2_stateful_decoder: Check H264 NALU type

Add a test to make sure the leading H.264 NALU type is expected. This
will help avoid falsely identifying H.265 Annex-B bitstreams as H.264.

BUG=b:227248846
TEST=tast run ${DUT} video.PlatformDecoding.v4l2_h264*

Change-Id: I6342ee6791d8687c1528f8fe6bdbdcce9ef9519c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/drm-tests/+/3573380
Tested-by: Nathan Hebert <nhebert@chromium.org>
Reviewed-by: Fritz Koenig <frkoenig@chromium.org>
Commit-Queue: Nathan Hebert <nhebert@chromium.org>
2 files changed