Simplify {,Set}UlpfecConfig interface.

webrtc/modules/rtp_rtcp/include/rtp_rtcp.h

Index: webrtc/modules/rtp_rtcp/include/rtp_rtcp.h
diff --git a/webrtc/modules/rtp_rtcp/include/rtp_rtcp.h b/webrtc/modules/rtp_rtcp/include/rtp_rtcp.h
index cbf953db0fd97a4bc8fecd7831d323ccbfa65b04..b8d873db4245c838117328334e2b666839073299 100644
--- a/webrtc/modules/rtp_rtcp/include/rtp_rtcp.h
+++ b/webrtc/modules/rtp_rtcp/include/rtp_rtcp.h
@@ -453,9 +453,16 @@ class RtpRtcp : public Module {
   // Video
   // **************************************************************************
 
-  // Turn on/off ULPFEC.
-  virtual void SetUlpfecConfig(bool enabled,
-                               int red_payload_type,
+  // Set RED and ULPFEC payload types. A payload type of -1 means that the
+  // corresponding feature is turned off. Note that we DO NOT support enabling
+  // ULPFEC without enabling RED. However, we DO support enabling RED without
+  // enabling ULPFEC. This is due to an RED/RTX workaround, where the receiver
+  // assumes that RTX packets carry RED if RED has been configured in the SDP,
+  // regardless of what RTX payload type mapping was negotiated in the SDP.
+  // TODO(brandtr): Update this comment when we have removed the RED/RTX
+  // send-side workaround, i.e., when we do not support enabling RED without
+  // enabling ULPFEC.
+  virtual void SetUlpfecConfig(int red_payload_type,
                                int ulpfec_payload_type) = 0;
 
   virtual int32_t SetFecParameters(const FecProtectionParams* delta_params,