Add disableNetworkTime config property

This was removed as part of this bug because the config wasn't used:

    Bug 64052650
    Change-Id I5c8ed3f0e78c2ed0d2e733939a82e1ab8940de22

This is now needed by Android Automotive since the network module may
live off board in a vehicle.

Bug: 110800197
Test: make & flash
Change-Id: I3715602e7fb22503d6867b61c22bdcb963174059