Add RtpPacketInfo to hold information about a received RtpPacket.

This change adds classes so that we later can plumb information about received packets to each audio and video frame. It's not wired up to do anything yet.

Bug: webrtc:10668
Change-Id: I962df493a76692f668314f78d6792d7636c5a31b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/138203
Commit-Queue: Chen Xing <chxg@google.com>
Reviewed-by: Minyue Li <minyue@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28138}
diff --git a/api/rtp_headers.h b/api/rtp_headers.h
index 44972ec..a7ae5cd 100644
--- a/api/rtp_headers.h
+++ b/api/rtp_headers.h
@@ -51,7 +51,7 @@
   absl::optional<FeedbackRequest> feedback_request;
 
   // Audio Level includes both level in dBov and voiced/unvoiced bit. See:
-  // https://datatracker.ietf.org/doc/draft-lennox-avt-rtp-audio-level-exthdr/
+  // https://tools.ietf.org/html/rfc6464#section-3
   bool hasAudioLevel;
   bool voiceActivity;
   uint8_t audioLevel;