Fix sending audio levels in conf call using zrtp

src/net/java/sip/communicator/impl/neomedia/transform/csrc/CsrcTransformEngine.java

@@ -137,6 +137,12 @@ public RawPacket reverseTransform(RawPacket pkt)
      */
     public synchronized RawPacket transform(RawPacket pkt)
     {
+        // if somebody has modified the packet and added an extension 
+        // don't process it. As ZRTP creates special rtp packets carring no
+        // rtp data and those packets are used only by zrtp we don't use them. 
+        if(pkt.getExtensionBit())
+            return pkt;
+
         long[] csrcList = mediaStream.getLocalContributingSourceIDs();
 
         if(csrcList == null || csrcList.length == 0)