airo: use ndo_siocdevprivate

The airo driver overloads SIOCDEVPRIVATE ioctls with another
set based on SIOCIWFIRSTPRIV. Only the first ones actually
work (also in compat mode) as the others do not get passed
down any more.

Change it over to ndo_siocdevprivate for clarification.

Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: linux-wireless@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>