IpManagerTest: fix flaky test

Reset the callback mock for every onLinkPropertiesChange expected when
pushing address updates on the BaseNetworkObserver.

Bug: 32561414
Bug: 62918393
Test: runtest frameworks-net, IpManagerTest passes 200 times in a row
Change-Id: I4719b4dc86044438243887634191c2d21686b80f
1 file changed