at::native batch norm kernel launch config update (#17047)
Summary:
limit block dimension to avoid configuration error on batch norm kernel launch
This should resolve #16998
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17047
Differential Revision: D14142132
Pulled By: soumith
fbshipit-source-id: 9c8c52dcd1d108cda1f65f5227e625b8fe6e12a0
