Modify Vpn#getNetId() to Vpn#getNetwork() and uses NETID_UNSET
when getNetwork() returns null in ConnectivityServiceTest.
Bug: 182963397
Test: atest FrameworksNetTests
Change-Id: I69d449705b1dc541287c72af8dc7705dc4733109
Merged-In: I69d449705b1dc541287c72af8dc7705dc4733109
(cherry-picked from ag/13927650)