message: Surface the number of threads used by ctx->runner() for numa_map_and_batch_dataset_op.cc
diff: @@ -201,7 +201,7 @@ class NumaMapAndBatchDatasetOp : public UnaryDatasetOpKernel {
  Status Initialize(IteratorContext* ctx) override {
  mutex_lock l(*mu_);
  if (num_parallel_calls_->value == kAutoTune) {
  - num_parallel_calls_->value = port::NumSchedulableCPUs();
  + num_parallel_calls_->value = ctx->runner_threadpool_size();
  num_parallel_calls_->tunable = true;
  }
  TF_RETURN_IF_ERROR(
  