Improve test coverage for disconnecting networks with clat.

Ensure that NetworkCallbacks and netd operations are accounted
for. Also add a test for the spurious onLinkPropertiesChanged
callback that is currently send out after onLost.

Bug: 176496580
Test: atest ConnectivityServiceTest
Change-Id: I69cf58bc87dfe55ea359a2cd76167d03fe2c953d
1 file changed