CodecMunger.UpdateAndGet returned a freshly allocated slice for every
forwarded packet on every down track. Return the header in a fixed array
with a length instead and marshal into it with MarshalTo. TranslationParams
carries the array; WriteRTP slices it locally.
UpdateAndGet now allocates zero times per call (was one). Escape analysis
confirms TranslationParams stays on the stack.
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>
* Do codec munging when munging RTP header.
It was possible for probe packets to get in between RTP munging and
codec munging and throw off sequence number while dropping packets.
Affected only VP8 as it does codec munging.
* do not pass in buffer as it is created anyway
* flip fields
* flip order
* fix test
* call translate for all tracks
* simplify
