Nvv4l2h264enc returns frames in wrong order when PTS doesn't align with framerate

[kudryavtsev_ia]

Hello, we develop Savant: a general-purpose high-level CV framework on DeepStream. Thus we test various functions and need them to work properly. The one function is conditional video encoding which is affected by the bug. Our developer implemented a workaround rearranging the frames properly on Jetson, but we believe it is beneficial to fix it in the core.