Extend isH264IDRStart to handle STAP-A aggregates (NAL type 24, RFC 6184
§5.7.1). The first NAL in the aggregate starts at byte 3 (after the
2-byte size field); if its type is 5 (IDR slice) the packet is treated
as an IDR start and the burst cache is reset.
This closes the gap noted in NOTES.md: a publisher using STAP-A for IDR
(e.g. a custom GStreamer pipeline or hardware encoder) will now correctly
reset the burst rather than accumulating packets until hitting the 512-
packet / 2 MiB capacity cap.
ZGaetano
8266ca72e6