Move Inet[4]AddressUtils to libs/net

The classes should not be picked up from frameworks/base, as they are
part of several mainline modules.

Bug: 151052811
Test: m; manual: flashed, wifi and telephony working
Test: atest NetworkStackCoverageTests
(clean cherry-pick from internal branch)
Merged-In: I62da3419408b7eb71ea5319e8717fbb22c76a94e

Change-Id: I62da3419408b7eb71ea5319e8717fbb22c76a94e