Added weight initialization for ConvTBC (#3179)
Added weight initialization for ConvTBC (#3179)

Summary:
# Before submitting

- [x] Was this discussed/approved via a Github issue? (no need for typos, doc improvements)
- [x] Did you read the [contributor guideline](https://github.com/pytorch/fairseq/blob/master/CONTRIBUTING.md)?
- [ ] Did you make sure to update the docs?
- [ ] Did you write any new necessary tests?

## What does this PR do?
Fixes https://github.com/pytorch/fairseq/issues/3131

## PR review
Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

## Did you have fun?
Make sure you had fun coding �

Pull Request resolved: https://github.com/pytorch/fairseq/pull/3179

Reviewed By: huihuifan

Differential Revision: D26225878

Pulled By: myleott

fbshipit-source-id: 52267d10db6ec86be1c89207a768ae8b54ae1f82

pytorch/fairseq,pytorch/fairseq,pytorch/fairseq