Switch to using list-of-subIds for VCN selection of underlying networks

This change switches from primarily using unwanted(NOT_VCN_MANAGED) to
list-of-subIds. This opens the door for a soft-start, predicated on the
VCN-exposed networks not populating their respective subId fields.

Allowing the potential for soft-start means that the VCN can exit safe
mode without carrier app intervention, when all requested configurations
are active.

Bug: 183174340
Test: atest FrameworksVcnTests
Change-Id: I57ecf4f5f04dc5d15589b17d647661674595b872