Don't log errors on a=rtcp lines

The a=rtcp:9 IN IP4 0.0.0.0 line is required by JSEP to be generated,
but is also required to be ignored. This reduces log spew.

Bug: None
Change-Id: I984060d9693b9df4c4cfdf2c5dea0ea620f4bc83
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/196641
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Philipp Hancke <philipp.hancke@googlemail.com>
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32798}
diff --git a/pc/webrtc_sdp.cc b/pc/webrtc_sdp.cc
index 7bd11aa..6f91d63 100644
--- a/pc/webrtc_sdp.cc
+++ b/pc/webrtc_sdp.cc
@@ -3274,6 +3274,10 @@
         }
 
         simulcast = error_or_simulcast.value();
+      } else if (HasAttribute(line, kAttributeRtcp)) {
+        // Ignore and do not log a=rtcp line.
+        // JSEP  section 5.8.2 (media section parsing) says to ignore it.
+        continue;
       } else {
         // Unrecognized attribute in RTP protocol.
         RTC_LOG(LS_INFO) << "Ignored line: " << line;