h264parse: update src caps with sps in case of byte-stream/nal earlier
Submitted by Hyunjun Ko
Since it starts a bit of buffering in byte-stream/nal, we can parse sps at preroll time. So I propose this patch.
This makes decodebin to be able to judge if a decoder is available or not at preroll time.
But I'm not sure this makes sense.
Need for review.