tulip: use ndo_siocdevprivate

The tulip driver has a debugging method over ioctl built-in, but it
does not actually check the command type, which may end up leading
to random behavior when trying to run other ioctls on it.

Change the driver to use ndo_siocdevprivate and limit the execution
further to the first private command code. If anyone still has tools
to run these debugging commands, they might have to be patched for
it if they pass different ioctl command.

The function has existed in this form since the driver was merged in
Linux-1.1.86.

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