fix(JSPC): local tracks not advertised

In case when the answer is being set for the first time, full sRD/sLD
cycle is required to have the local description updated and SSRCs
synchronized correctly. Otherwise SSRCs for streams added after invite,
but before the answer was accepted will not be detected. The reason for
that is that renegotiate can not be called when adding tracks and they
will not be reflected in the local SDP.

modules/xmpp/JingleSessionPC.js

@@ -1557,7 +1557,16 @@ export default class JingleSessionPC extends JingleSession {
             this.peerconnection.setRemoteDescription(
                 remoteDescription,
                 () => {
-                    resolve();
+                    // In case when the answer is being set for the first time,
+                    // full sRD/sLD cycle is required to have the local
+                    // description updated and SSRCs synchronized correctly.
+                    // Otherwise SSRCs for streams added after invite, but
+                    // before the answer was accepted will not be detected.
+                    // The reason for that is that renegotiate can not be called
+                    // when adding tracks and they will not be reflected in
+                    // the local SDP.
+                    this._initiatorRenegotiate(
+                        remoteDescription, resolve, reject);
                 },
                 error => reject(`setRemoteDescription failed: ${error}`)
             );