Negotiate use of RTCP loss notification feedback (LNTF)

When the LossNotifications field trial is in effect, LNTF should
be offered/accepted in the SDP message, not assumed to be configured
on both sides equally.

Bug: webrtc:10662
Change-Id: Ibd827779bd301821cbb4196857f6baebfc9e7dc2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/138079
Commit-Queue: Elad Alon <eladalon@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28056}
diff --git a/call/video_receive_stream.h b/call/video_receive_stream.h
index 5a819f9..63fc5b7 100644
--- a/call/video_receive_stream.h
+++ b/call/video_receive_stream.h
@@ -179,6 +179,9 @@
       // See draft-holmer-rmcat-transport-wide-cc-extensions for details.
       bool transport_cc = false;
 
+      // See LntfConfig for description.
+      LntfConfig lntf;
+
       // See NackConfig for description.
       NackConfig nack;