smb: move cifs_xattr_handlers to .rodata

smb: move cifs_xattr_handlers to .rodata

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

Cc: Steve French <sfrench@samba.org>
Cc: Paulo Alcantara <pc@manguebit.com>
Cc: Ronnie Sahlberg <lsahlber@redhat.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: linux-cifs@vger.kernel.org
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
Link: https://lore.kernel.org/r/20230930050033.41174-24-wedsonaf@gmail.com
Reviewed-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>