kernfs: attach uuid for every kernfs and report it in fsid

The following two commits added the same thing for tmpfs:

* commit 2b4db796 ("tmpfs: generate random sb->s_uuid")
* commit 59cda49e ("shmem: allow reporting fanotify events with file handles on tmpfs")

Having fsid allows using fanotify, which is especially handy for cgroups,
where one might be interested in knowing when they are created or removed.

Signed-off-by: Ivan Babrou <ivan@cloudflare.com>
Acked-by: Jan Kara <jack@suse.cz>
Acked-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20230731184731.64568-1-ivan@cloudflare.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>