Use the copy_from_user() and copy_to_user() functions for accessing
memory provided by the user in the ptm netdev iotls.
In addition also check for root permission before executing ioctl.
Suggested-by: Stanislav Fort from Aisle Research
Reported-by: Stanislav Fort from Aisle Research
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>