Stop playing games with the namespace id and use a boolean instead: * This will remove the special-casing we need to do everywhere for mount namespaces. * It will allow us to use asserts on the namespace id for initial namespaces everywhere. * It will allow us to put anonymous mount namespaces on the namespaces trees in the future and thus make them available to statmount() and listmount(). Link: https://patch.msgid.link/20251110-work-namespace-nstree-fixes-v1-10-e8a9264e0fb9@kernel.org Signed-off-by: Christian Brauner <brauner@kernel.org>