add defaults again after importing user_module (facebookresearch#3007)

Summary:
## What does this PR do?
Default values for the configs imported from `user_dir` was not added properly.

Pull Request resolved: https://github.com/fairinternal/fairseq-py/pull/3007

Reviewed By: alexeib

Differential Revision: D33926315

Pulled By: wnhsu

fbshipit-source-id: 914eecec769964686342d66c96d6ba76f12e1277

fairseq_cli/train.py

@@ -31,6 +31,7 @@
 from fairseq.data import data_utils, iterators
 from fairseq.data.plasma_utils import PlasmaStore
 from fairseq.dataclass.configs import FairseqConfig
+from fairseq.dataclass.initialize import add_defaults
 from fairseq.dataclass.utils import convert_namespace_to_omegaconf
 from fairseq.distributed import fsdp_enable_wrap, fsdp_wrap
 from fairseq.distributed import utils as distributed_utils
@@ -45,6 +46,7 @@ def main(cfg: FairseqConfig) -> None:
         cfg = convert_namespace_to_omegaconf(cfg)
 
     utils.import_user_module(cfg.common)
+    add_defaults(cfg)
 
     if (
         distributed_utils.is_master(cfg.distributed_training)