The downstream do not be tracked if PrivateAddressCoordinator just
return cached address. Then, PrivateAddressCoordinator would not notify
that downstream if conflict happen.
Also remove the null check in getDownstreamPrefix because:
- An IpServer is only added to mDownstreams by requestDownstreamAddress.
- That method will only add the IpServer to mDownstreams if it has an
IPv4 address.
- As soon as that method returns, the IpServer sets mIpv4Address to the
address that was returned.
- When an IpServer is torn down, mIpv4Address is set to null after
releaseDownstream is called.
So it should never be possible for this to return null.
Bug: 168169687
Test: atest CtsTetheringTest
atest TetheringTests
Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1459887
Change-Id: I4b4d75c8a4f1de07aa7bb68b12d150d7c85c9cc1
Merged-In: Ide5206b013acdc499344e1c839a830c5b245af41
(cherry picked from commit 0854becd64)
2bafaf0dfe