Make the IP subnet persistent till reboot

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 8cef61a1b2119caaabb9e672451f3a2ab07d589c)