[BUG] in rpc callback no telemetry or attributes can be sent

[longGr]

When a RPC_Callback is executed and within that method, a sendTelemtry or sendAttribute is executed, the response of the RPC is lost and the thingsboard server gets a timeout.

Steps to reproduce:

RPC_Response do_something(const RPC_Data & data) {
  tb.sendTelemetryInt("status", 0);
  return RPC_Response("success", true);
}

in the example. the response seems to be lost. When running the RPC request via swagger-ui, the command times out.