ext4: move ext4_xattr_handlers to .rodata

This makes it harder for accidental or malicious changes to
ext4_xattr_handlers at runtime.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: linux-ext4@vger.kernel.org
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
Link: https://lore.kernel.org/r/20230930050033.41174-3-wedsonaf@gmail.com


Signed-off-by: Christian Brauner <brauner@kernel.org>