Make the IP subnet persistent if it do not conflict with upstream. It allow client to reuse its IP that usually reduce DHCP procedure. Bug: 168169687 Test: atest TetheringTests Change-Id: Iddc5304730dce7b11c5d124b7eddce057d752bbd Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1432958 Change-Id: I60ed54651034f21ca1cd253d272ac3478881b4e0 Merged-In: Iddc5304730dce7b11c5d124b7eddce057d752bbd (cherry picked from commit 177e2d8d1867d7e72d00c81d6fbbed756c9f0568)