libceph: weaken sizeof check in ceph_x_verify_authorizer_reply()

commit f1d10e04637924f2b00a0fecdd2ca4565f5cfc3f upstream.

Allow for extending ceph_x_authorize_reply in the future.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Sage Weil <sage@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>