for (partially) parsing DTLS packets and extracting the msg_seqs BUG=webrtc:367395350 Change-Id: Ieb0fc121c6dc82118ced5939c1a9ebe2d72e3cb3 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/370181 Commit-Queue: Philipp Hancke <phancke@meta.com> Reviewed-by: Harald Alvestrand <hta@webrtc.org> Reviewed-by: Jonas Oreland <jonaso@webrtc.org> Cr-Commit-Position: refs/heads/main@{#43501}