@Override
  public void setRPCPacket(Message param) {
    this.packet = param;
  }
Gives this instance a reference to the protobuf received by the RPC, so that it can later
compute its size if asked for it.
@param param The protobuf received by the RPC for this call
hbase-server/src/main/java/org/apache/hadoop/hbase/monitoring/MonitoredRPCHandlerImpl.java