Save old TCC feedback timestamps, in case of packet reordering.

Based on libwebrtc's equivalent code (as used in Chrome).

src/main/kotlin/org/jitsi/nlj/transform/node/incoming/TccGeneratorNode.kt

@@ -92,10 +92,11 @@ class TccGeneratorNode(
     private fun addPacket(tccSeqNum: Int, timestamp: Long, isMarked: Boolean, ssrc: Long) {
         synchronized(lock) {
             if (packetArrivalTimes.ceilingKey(windowStartSeq) == null) {
-                // Packets in map are all older than the start of the next tcc feedback packet,
-                // remove them
-                // TODO: Chrome does something more advanced, keeping older sequences to replay on packet reordering.
-                packetArrivalTimes.clear()
+                // Start new feedback packet, cull old packets.
+                packetArrivalTimes.entries.removeIf {
+                    entry -> entry.key < tccSeqNum &&
+                        timestamp - entry.value >= BACK_WINDOW_MS
+                }
             }
             if (windowStartSeq == -1 || tccSeqNum < windowStartSeq) {
                 windowStartSeq = tccSeqNum
@@ -183,4 +184,10 @@ class TccGeneratorNode(
             addBoolean("enabled", enabled)
         }
     }
+
+    companion object {
+        /** The number of milliseconds of old tcc reports to save */
+        /** TODO: Chrome makes this a field trial param; do we need to make it configurable? */
+        private val BACK_WINDOW_MS = 500
+    }
 }