appletalk: use ndo_siocdevprivate

appletalk has three SIOCDEVPRIVATE ioctl commands that are
broken in compat mode because the passed structure contains
a pointer.

Change it over to ndo_siocdevprivate for consistency and
make it return an error when called in compat mode. This
could be fixed if there are still users.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>