title: TableView frame being reset on some devices
body: <p>I have a UIViewController that contains a TableView and an GADBannerView at the bottom. When an ad is received I change the height of the TableView so the ad doesn't cover any cells. This worked without any problem on my iPhone 6 (iOS 10) and in the simulators (iOS 10), but for some reason when testing my app on an old iPhone 4s (iOS 9), the TableView height gets reset if I leave the view controller and then return to it. Why does this happen and how can I prevent it?</p>
  
  <p>This is the code I use to resize the tableview.</p>
  
  <pre><code>- (void)adViewDidReceiveAd:(GADBannerView *)view {
  
     if (!adRecieved) {
  
      view.hidden = NO;
      CGRect currentRect = self.tableView.frame;
      currentRect.size.height -= CGRectGetHeight(view.frame);
      self.tableView.frame = currentRect;
  
      adRecieved = YES;
  }
  </code></pre>