Rename BROADCAST_SCORE_NETWORKS to BROADCAST_NETWORK_PRIVILEGED.

This is necessary/desired for two reasons:

1. UX around network scoring shipped with L despite lacking underlying
platform support. We do not want network scoring applications to
trigger this UX on L devices, and therefore we must break the contract
of what defines a network scorer so that apps build against the new
contract don't trigger the old UX.

2. As a start towards generalizing the term "score" for a potentially
broader role in the future, though that role is very much undefined.

Bug: 18160480
Change-Id: If228977513e32e45bc44dbeda24aa18436fdfca6