Enable `--num-batch` by default (#2157)
Summary:
Pull Request resolved: https://github.com/pytorch/benchmark/pull/2157
By default, we can enable `--num-batch` option for all models by always returning the same batch of input.
Reviewed By: ckluk2
Differential Revision: D53549476
fbshipit-source-id: bdd7ce782494484530cc9dba1b870cdcebcb4554
