In RtcpReceiver implement calling NetworkLinkRtcpObserver interface

With intent to fully replace RtcpBandwidthObserver interface
and half of the TransportFeedbackObserver interface

RtcpBandwidthObserver interfaces passed bitrate and time variables as
raw ints, NetworkLinkRtcpObserver uses more expressive types.

Bug: webrtc:13757, webrtc:8239
Change-Id: I0a8c8de626fbe0c190a0a1a9f6733d863494401c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/304700
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#40043}
diff --git a/modules/rtp_rtcp/source/rtp_rtcp_interface.h b/modules/rtp_rtcp/source/rtp_rtcp_interface.h
index ebd16ee..6e62bf8 100644
--- a/modules/rtp_rtcp/source/rtp_rtcp_interface.h
+++ b/modules/rtp_rtcp/source/rtp_rtcp_interface.h
@@ -71,8 +71,14 @@
 
     // Called when we receive a changed estimate from the receiver of out
     // stream.
+    // TODO(bugs.webrtc.org/13757): Deprecated and Remove in favor of
+    // `network_link_rtcp_observer`
     RtcpBandwidthObserver* bandwidth_callback = nullptr;
 
+    // Called when receive an RTCP message related to the link in general, e.g.
+    // bandwidth estimation related message.
+    NetworkLinkRtcpObserver* network_link_rtcp_observer = nullptr;
+
     NetworkStateEstimateObserver* network_state_estimate_observer = nullptr;
     TransportFeedbackObserver* transport_feedback_callback = nullptr;
     VideoBitrateAllocationObserver* bitrate_allocation_observer = nullptr;