Don't skip_torchrec when using torchrec PT2 pipeline (pytorch#2298)

Summary:
Pull Request resolved: pytorch#2298

We introduced `torch._dynamo.config.skip_torchrec` to control whether tracing into torchrec paths. PT2 pipeline is mainly used for torchrec PT2 compilation, so it should set `skip_torchrec` to False by default

Reviewed By: IvanKobzarev

Differential Revision: D61219995

torchrec/distributed/train_pipeline/train_pipelines.py

@@ -248,6 +248,7 @@ def progress(self, dataloader_iter: Iterator[In]) -> Out:
                 torch._dynamo.config.force_unspec_int_unbacked_size_like_on_torchrec_kjt = (
                     True
                 )
+                torch._dynamo.config.skip_torchrec = False
 
                 # Importing only before compilation to not slow-done train_pipelines import
                 torch.ops.import_module("fbgemm_gpu.sparse_ops")