Update native_functions.yaml to add DefaultBackend. (#45938)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/45938
Test Plan: Imported from OSS
Reviewed By: ezyang
Differential Revision: D24165889
Pulled By: ailzhang
fbshipit-source-id: 7f3ccdb3499b40795bc34af716d0e63241ae8de3
