Protection against early rtcp packets.
If recieve rtcp packets early then funnel is not ready, And there will be a GST_FLOW_FLUSHING returned when pushing data to it's srcpad. This cause thread that handle rtcp packets to go to pause mode. Since this thread is in pause mode there will be no callback that handle keep alive for incomming rtcp packets.This will make the session going down if client is not using other keep alive mecanism.
Change-Id: I992f8132cfa8be58ff894142df190a88453c803a