hippi: use ndo_siocdevprivate

The rr_ioctl uses private ioctl commands that correctly pass
all data through ifr_data, which works fine in compat mode.

Change it to use ndo_siocdevprivate as a cleanup.

Cc: Jes Sorensen <jes@trained-monkey.org>
Cc: linux-hippi@sunsite.dk
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>