kernfs: move kernfs_xattr_handlers to .rodata

This makes it harder for accidental or malicious changes to
kernfs_xattr_handlers at runtime.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
Link: https://lore.kernel.org/r/20230930050033.41174-18-wedsonaf@gmail.com


Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>