[Onnxifi] Add initializers to the C2 net passed into Glow (#35764)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35764
So that Glow knows what input is constant.
We probably need to do similar things to torch_glow though.
Test Plan:
```
buck build caffe2/caffe2/opt/custom:glow_net_transform
```
Reviewed By: jackm321
Differential Revision: D20770514
fbshipit-source-id: d398eb8eddbdbba21ccb5b4ac9cb335e4b27b8b3
