title: getNetworkPrefixLength() returns strange subnet mask
body: <p>The following code:</p>
  
  <pre><code>InetAddress localHost = Inet4Address.getLocalHost();
  NetworkInterface networkInterface = NetworkInterface.getByInetAddress(localHost);
  
  for (InterfaceAddress address : networkInterface.getInterfaceAddresses()) {
      System.out.println(address.getAddress() + "/" + address.getNetworkPrefixLength());
  }
  </code></pre>
  
  <p>returns:</p>
  
  <pre><code>/fe80:0:0:0:11da:433a:412a:8c23%13/64
  /192.168.1.107/128
  </code></pre>
  
  <p>My subnet mask is /24, not /128. Is it a Java bug?</p>