Adding rtcp report interval into RTCConfiguration.

This is a follow up of https://webrtc-review.googlesource.com/c/src/+/43201.

Issue 43201 didn't do the job properly.
1. The audio rtcp report interval is not properly hooked up.
2. We don't need to propagate audio rtcp interval into video send stream or vice versa.
3. We don't need to propagate rtcp report interval to any receiving streams.

Bug: webrtc:8789
Change-Id: I1f637d6e5173608564ef0702d7eda6fc93b3200f
Reviewed-on: https://webrtc-review.googlesource.com/c/110105
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Magnus Flodman <mflodman@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Jiawei Ou <ouj@fb.com>
Cr-Commit-Position: refs/heads/master@{#25610}
diff --git a/audio/audio_send_stream_unittest.cc b/audio/audio_send_stream_unittest.cc
index 6a92329..ed94283 100644
--- a/audio/audio_send_stream_unittest.cc
+++ b/audio/audio_send_stream_unittest.cc
@@ -334,11 +334,12 @@
   config.rtp.extmap_allow_mixed = true;
   config.rtp.extensions.push_back(
       RtpExtension(RtpExtension::kAudioLevelUri, kAudioLevelId));
+  config.rtcp_report_interval_ms = 2500;
   EXPECT_EQ(
       "{rtp: {ssrc: 1234, extmap-allow-mixed: true, extensions: [{uri: "
       "urn:ietf:params:rtp-hdrext:ssrc-audio-level, id: 2}], nack: "
-      "{rtp_history_ms: 0}, c_name: foo_name}, send_transport: null, "
-      "media_transport: null, "
+      "{rtp_history_ms: 0}, c_name: foo_name}, rtcp_report_interval_ms: 2500, "
+      "send_transport: null, media_transport: null, "
       "min_bitrate_bps: 12000, max_bitrate_bps: 34000, "
       "send_codec_spec: {nack_enabled: true, transport_cc_enabled: false, "
       "cng_payload_type: 42, payload_type: 103, "