Allowing buffering a LNTF (loss notification) feedback message in RTCPSender

Loss notifications may either be sent immediately, or wait until another
RTCP feedback message is sent.

Bug: webrtc:10336
Change-Id: I40601d9fa1dec6c17b2ce905cb0c8cd2dcff7893
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/139242
Commit-Queue: Elad Alon <eladalon@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28142}

modules/rtp_rtcp/include/rtp_rtcp.h

@@ -435,7 +435,8 @@ class RtpRtcp : public Module, public RtcpFeedbackSenderInterface {
   // Returns -1 on failure else 0.
   virtual int32_t SendLossNotification(uint16_t last_decoded_seq_num,
                                        uint16_t last_received_seq_num,
-                                       bool decodability_flag) = 0;
+                                       bool decodability_flag,
+                                       bool buffering_allowed) = 0;
 };
 
 }  // namespace webrtc