staging: wlan-ng: use siocdevprivate

wlan-ng has two private ioctls that correctly work in compat
mode. Move these over to the new ndo_siocdevprivate mechanism.

The p80211netdev_ethtool() function is commented out and
has no use here, so this can be removed

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