Stop calling setAlwaysOnPackage from VpnManagerService

To decouple VpnManagerService from ConnectivityServiceTest, stop
calling setAlwaysOnPackage from VpnManagerService as a
preparation for the follow up changes. Update it to equivalent
calls from Vpn directly.

The VpnManagerService variable is still needed because tests
have indirect calls via sending intent to update the lock
down behavior.

Bug: 230548427
Test: atest ConnectivityServiceTest
Change-Id: Ib78ac8173b2a4d2a8e9845e943eb63d79c36218c
1 file changed