Create LockdownVpnTrackerTest

Create unit tests for LockdownVpnTracker in a new test class in
order to move it out of ConnectivityServiceTest.

Bug: 230548427
Test: atest LockdownVpnTrackerTest
Change-Id: I85a324d9d7624e1f3638bdf64b054f0b3f9c5b8d
1 file changed