Use native code to convert IP addresses to strings.

Use native code to convert IP addresses to strings.

- Add a byteArrayToIpString method to the INetworkSystem interface and implement
  it in native code
- Fix the native code so it does better error reporting
- Change InetAddress's getHostAddress, getHostName and getCanonicalHostName
  methods to use it and remove the IPv4-only Java implementations
- Remove Inet6Util.createIPAddrStringFromByteArray
- Fix InetAddress so getByAddress(null) throws UnknownHostException instead of
  NullPointerException for compatibility with the RI.

Change-Id: I26548922e9eed63b295173456183c4ab3ce20718