Replace NetworkUtils methods

NetworkUtils is moved to connectivity mainline module which is
not accessible for module outside. getNetworkPart() method is
used by wifi lib and Settings but no usage inside the module,
so move the method to framework lib to share with wifi lib and
Settings.

Also, NetworkUtils.numericToInetAddress() method is also hidden
and deprecated. It should be replaced by
InetAddresses.parseNumericAddress().

Update the corresponding usage to refer to these methods.

Bug: 172183305
Test: atest SettingsRoboTests
Change-Id: I2fb674e0d7da0b11ba70177853fd6259bce372a3