apns: NOS: fix tethering and mms.

  This fixes BUGBASH-2328 for Portuguese carrier NOS (mcc="268"
  mnc="03").

  This is an ugly workaround since you can't edit the APN definition
  anymore: if you try to save an APN with type dun, you get the error
  message: "Carrier does not allow adding APNs of type dun." But it's
  working.

  Since the preinstalled APNs does not need to be edited and this
  doesn't break anything else for this carrier, this is acceptable.

  Thanx to tfae@xda.

Change-Id: Ic81a9549bf9610805e68b9be56c811b008cbdacb