Randomize the local Wifi IPv4 address

Also: address a few "error prone" warnings, adding @Override where missing

Test: as follows
    - built, flashed, booted
    - runtest frameworks-net passes (with --no-hidden-api-checks)
    - wifi tethering uses a randomized address, in as much as it can work
Bug: 32163131
Bug: 70673901

Change-Id: Icfabc48f2cf97b362ce292747f47021e84b900da