cleanup - config_item_ip() and DEFAULT_IPV4_LOCAL_SUBNET am: 36f4665ab4 am: 5350b6302f

Original change: https://googleplex-android-review.googlesource.com/c/platform/external/android-clat/+/11736256

Change-Id: I8948421a00c8c4dbaca40e9cff53ff70db34ab6e