Run IpClientLinkObserver on Binder thread

This restores previous behavior, where callbacks would not be called on
the IpClient handler thread.

Test: atest FrameworksNetTests NetworkStackTests
Test: flashed, WiFi works
Bug: 123062477
Change-Id: I3015566b0922d76ac7cf70579a1de3e033bf7b4a
3 files changed