Add SetPayloadType to FlexfecReceiveStream.

This reduces the number of times we recreate video receive streams
and prepares for not having to do that for flexfec streams and avoid
having to recreate a video receive stream when flexfec config changes.

Bug: webrtc:11993
Change-Id: I11134b6a72eb162623ebbc12521d409da8616107
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261941
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37641}
diff --git a/call/flexfec_receive_stream.h b/call/flexfec_receive_stream.h
index 7c8cd2e..4f6fe44 100644
--- a/call/flexfec_receive_stream.h
+++ b/call/flexfec_receive_stream.h
@@ -65,6 +65,10 @@
   // Perhaps this should be in ReceiveStreamInterface and apply to audio streams
   // as well (although there's no logic that would use it at present).
   virtual void SetRtcpMode(RtcpMode mode) = 0;
+
+  // Called to change the payload type after initialization.
+  virtual void SetPayloadType(int payload_type) = 0;
+  virtual int payload_type() const = 0;
 };
 
 }  // namespace webrtc