ClatCoordinatorTest: add test for startClat error handling

Used to increase mainline test code coverage for startClat()
which has bunches of code for unwinding the native method failure.

For now, code coverage for startClat(): 51.89% (55/106 lines)

Test: atest com.android.server.connectivity.ClatCoordinatorTest
Change-Id: I398d5863359ff329b06966488053edd9006f17aa
1 file changed