this preps other work, which may or may not be the recent reviews by @olce.freebsd_certner.fr
> commit 35346230e6186214874c823bb84baea9b3499ec0
> Author: Mateusz Guzik <mjg@FreeBSD.org>
> Date: Wed Jul 5 23:01:17 2023 +0000
>
> vfs: factor out mount point traversal to a dedicated routine
>
> While here tidy up asserts in the area.
>
> Reviewed by:
> Differential Revision:
>
> commit 21bc84b65b389cc047b3d87b8112adb0df6504cf
> Author: Mateusz Guzik <mjg@FreeBSD.org>
> Date: Wed Jul 5 22:56:04 2023 +0000
>
> vfs: stop passing LK_RETRY with LK_UPGRADE in vfs_lookup
>
> vn_lock already returns the expected error.
>
> Reviewed by:
> Differential Revision: