Move RtpExtension to api/ directory and config.h/.cc to call/.

BUG=webrtc:5876
R=deadbeef@webrtc.org, solenberg@webrtc.org

Review-Url: https://codereview.webrtc.org/3004723002 .
Cr-Commit-Position: refs/heads/master@{#19639}
diff --git a/webrtc/api/BUILD.gn b/webrtc/api/BUILD.gn
index 3d19f03..e58f393 100644
--- a/webrtc/api/BUILD.gn
+++ b/webrtc/api/BUILD.gn
@@ -62,6 +62,7 @@
     "proxy.h",
     "rtcerror.cc",
     "rtcerror.h",
+    "rtpparameters.cc",
     "rtpparameters.h",
     "rtpreceiverinterface.h",
     "rtpsender.h",
@@ -258,6 +259,7 @@
       "ortc/mediadescription_unittest.cc",
       "ortc/sessiondescription_unittest.cc",
       "rtcerror_unittest.cc",
+      "rtpparameters_unittest.cc",
     ]
 
     if (!build_with_chromium && is_clang) {