netfront: get IOCTL definitions from proper place

There were 2 places with ioctl definitions, Xen netfront driver
was compiled with IOCTL definitions from wrong place.

Fixed by changing include and deleting file with improper definitions

Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>