use F.batch_norm in FrozenBN, if not using autograd
use F.batch_norm in FrozenBN, if not using autograd

Reviewed By: wat3rBro

Differential Revision: D19079546

fbshipit-source-id: 4669b1dd2f6a182233cdc9c0c6530eddbd2eab5e

facebookresearch/detectron2,facebookresearch/detectron2,facebookresearch/detectron2