Implement review changes 2

modules/RTC/TraceablePeerConnection.js

 
     for (const mLine of mLines) {
         if (mLine.type === 'audio') {
-            const { payload } = mLine.rtp.find(protocol => protocol.codec === 'opus');
+            const { payload } = mLine.rtp.find(protocol => protocol.codec === CodecMimeType.OPUS);
 
             if (!payload) {
                 break;

service/RTC/CodecMimeType.js

 /* global module */
 /**
  * Enumeration of the codec mime types
- * @type {{H264: string, VP8: string, VP9: string}}
+ * @type {{H264: string, OPUS: string, VP8: string, VP9: string}}
  */
 const CodecMimeType = {
     /**
-     * The h264 codec mime type
+     * The h264 codec mime type.
      */
     H264: 'h264',
 
+    /**
+     * The opus codec mime type.
+     */
+    OPUS: 'opus',
+
     /**
      * The vp8 codec mime type.
      */