This is a no-op change to move some common codes that share between different VPN unit tests to the new base class. It's helpful to reduce the code duplication for the follow up work to add the VpnManagerServiceTest and other test codes refactor. Bug: 231373589 Test: atest FrameworksNetTests Change-Id: Id5111e7ca33ea8f9eb4bcc6c13d0e681f0664d24