Fix tcp connection cleanup and update stream from forward to mix fail issue (#802)

Author: qwu16

source/agent/conference/roomController.js

@@ -1614,7 +1614,7 @@ module.exports.create = function (spec, on_init_ok, on_init_failed) {
                             if (streamId) {
                                 streams[streamId][kind].subscriber = streams[streamId][kind].subscribers || [];
                                 streams[streamId][kind].subscribers.push(terminal_id);
-                                terminals[terminal_id].subscribed[subscriptionId].audio = streamId;
+                                terminals[terminal_id].subscribed[subscriptionId][kind] = streamId;
                             }
                         }
                         on_ok('ok');

source/agent/conference/subscription.js

@@ -105,6 +105,7 @@ class Subscription {
     this.media.tracks.forEach(track => {
       if (track.from === sourceId) {
         // Extract source track from stream
+        delete track.source;
         const source = stream.id === sourceId ?
           stream.media.tracks.find(t => t.type === track.type) :
           stream.media.tracks.find(t => t.id === sourceId);