Merge patch series "ovl: allow O_PATH file descriptor when specifying layers"

Christian Brauner <brauner@kernel.org> says:

Allow overlayfs to use O_PATH file descriptors when specifying layers.
Userspace must currently use non-O_PATH file desriptors which is often
pointless especially if the file descriptors have been created via
open_tree(OPEN_TREE_CLONE). This has been a frequent request and came up
again in [1].

Link: https://lore.kernel.org/r/fd8f6574-f737-4743-b220-79c815ee1554@mbaynton.com
* patches from https://lore.kernel.org/r/20250210-work-overlayfs-v2-0-ed2a949b674b@kernel.org:
  selftests/overlayfs: test specifying layers as O_PATH file descriptors
  fs: support O_PATH fds with FSCONFIG_SET_FD

Link: https://lore.kernel.org/r/20250210-work-overlayfs-v2-0-ed2a949b674b@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>