Bug 953

when a ss node moves out of range, it starts to scan 
void
SSLinkManager::StartScanning (
  SubscriberStationNetDevice::EventType type, bool deleteParameters)
{

...

  if (m_ss->GetState () != SubscriberStationNetDevice::SS_STATE_IDLE)
    {
      m_dlChnlNr++;
    }

however, if no base station is found, the above counter will overflow after 20 tries and segmentation fault will occur.  The value of 20 is due to the below code:

void
WimaxNetDevice::InitializeChannels (void)
{
  // initializing arbitrary vector of channels (or frequencies)
  uint64_t frequency = 2000;

  for (uint8_t i = 0; i < 20; i++)
    {
      m_dlChannels.push_back (frequency);
      frequency += 40;
    }
}

I started to provide a patch for this that:
- moved the magic number 20 into an attribute
- cause a check in the above scanning code so that it did not overflow

but one question I have is what should be the behavior if the max value is reached?  Stop scanning, restart immediately from channel 0, go to sleep for a while?  Please advise.

Also, can you please comment on whether the above frequency = 2000 assignment is still arbitrary and needs to be moved also to an attribute?  What defaults correspond to real implementations (frequency start, frequency increment, number of channels, etc.)?  In other words, can we remove the "arbitrary" from the above?