fix(JitsiConference): reset local tracks SSRCs on call ended

When call ends the PeerConnection is closed and the SSRCs stored in
the local track will not match those assigned the PeerConnection when
it's reopened for new session. This will confuse SSRC replacement logic.
We need to reset those SSRCs and re-register 'ssrcHandler' listener to
get the new ones.

JitsiConference.js

     if (this.statistics) {
         this.statistics.stopRemoteStats();
     }
+    // PeerConnection has been closed which means that SSRCs stored in
+    // JitsiLocalTrack will not match those assigned by the old PeerConnection
+    // and SSRC replacement logic will not work as expected.
+    // We want to re-register 'ssrcHandler' of our local tracks, so that they
+    // will learn what their SSRC from the new PeerConnection which will be
+    // created on incoming call event.
+    var self = this;
+    this.rtc.localTracks.forEach(function(localTrack) {
+        // Reset SSRC as it will no longer be valid
+        localTrack._setSSRC(null);
+        // Bind the handler to fetch new SSRC, it will un register itself once
+        // it reads the values
+        self.room.addListener(
+            XMPPEvents.SENDRECV_STREAMS_CHANGED, localTrack.ssrcHandler);
+    });
 };