Make RTCP report interval configurable

Bug: webrtc:8789
Change-Id: I79c9132123c946b030ed79c647b4329e81d6e6ae
Reviewed-on: https://webrtc-review.googlesource.com/43201
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Commit-Queue: Stefan Holmer <stefan@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21837}

modules/rtp_rtcp/include/rtp_rtcp.h

@@ -94,6 +94,7 @@ class RtpRtcp : public Module, public RtcpFeedbackSenderInterface {
     RateLimiter* retransmission_rate_limiter = nullptr;
     OverheadObserver* overhead_observer = nullptr;
     RtpKeepAliveConfig keepalive_config;
+    RtcpIntervalConfig rtcp_interval_config;
 
    private:
     RTC_DISALLOW_COPY_AND_ASSIGN(Configuration);