package/patch: fix xattr option

The name of the configure option is, and has always been,
 --enable-xattr, not --enable-attr. Otherwise, configure
whines:
    configure: WARNING: unrecognized options: --enable-attr

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>