code: func nicUnitRange(l object.VirtualDeviceList) (int, error) {
  	// No NICs means no range
  	if len(l) < 1 {
  		return 0, nil
  	}
  
  	high := int32(networkInterfacePciDeviceOffset)
  
  	for _, v := range l {
  		d := v.GetVirtualDevice()
  		if d.UnitNumber == nil {
  			return 0, fmt.Errorf("device at key %d has no unit number", d.Key)
  		}
  		if *d.UnitNumber > high {
  			high = *d.UnitNumber
  		}
  	}
  	return int(high - networkInterfacePciDeviceOffset + 1), nil
  }
docs: // nicUnitRange calculates a range of units given a certain VirtualDeviceList,
  // which should be network interfaces.  It's used in network interface refresh
  // logic to determine how many subresources may end up in state.