feat(RTC) added DTLS transport monitoring

modules/RTC/TraceablePeerConnection.js

      */
     this.remoteUfrag = null;
 
+    /**
+     * The DTLS transport object for the PeerConnection.
+     * Note: this assume only one shared transport exists because we bundled
+     *       all streams on the same underlying transport.
+     */
+    this._dtlsTransport = null;
+
     /**
      * The signaling layer which operates this peer connection.
      * @type {SignalingLayer}
     });
 };
 
+/**
+ * Sets up the _dtlsTransport object and initializes callbacks for it.
+ */
+TraceablePeerConnection.prototype._initializeDtlsTransport = function() {
+    // We are assuming here that we only have one bundled transport here
+    if (this._dtlsTransport) {
+        return;
+    }
+
+    const senders = this.peerconnection.getSenders();
+
+    if (senders.length !== 0 && senders[0].transport) {
+        this._dtlsTransport = senders[0].transport;
+
+        this._dtlsTransport.onerror = error => {
+            logger.error(`${this} DtlsTransport error: ${error}`);
+        };
+
+        this._dtlsTransport.onstatechange = () => {
+            this.trace('dtlsTransport.onstatechange', this._dtlsTransport.state);
+        };
+    }
+};
+
+
 /**
  * Configures the stream encodings depending on the video type and the bitrates configured.
  *
                     this.localUfrag = localUfrag;
                     this.eventEmitter.emit(RTCEvents.LOCAL_UFRAG_CHANGED, this, localUfrag);
                 }
+
+                this._initializeDtlsTransport();
+
                 resolve();
             }, err => {
                 this.trace('setLocalDescriptionOnFailure', err);
                     this.remoteUfrag = remoteUfrag;
                     this.eventEmitter.emit(RTCEvents.REMOTE_UFRAG_CHANGED, this, remoteUfrag);
                 }
+
+                this._initializeDtlsTransport();
+
                 resolve();
             }, err => {
                 this.trace('setRemoteDescriptionOnFailure', err);