Avoid overlapping NetIDs in ConnectivityServiceTest with real NetIDs

Overlapping the NetIDs can cause the ConnectivityService instance under test
to inadvertently use real networks, for example when NetworkMonitor attempts
to validate a network.  This fixes test hangs when run on devices with
active internet connections.

Change-Id: I5e1898953f0117b9f75beccac4a52ae2db173567