Map network identity using ConnectivityService.

Instead of deriving network identity based on raw subsystem broadcasts,
listen for updates from ConnectivityService.  Added atomic view of all
active NetworkState, and build map from "iface" to NetworkIdentity set
for stats tracking.

To avoid exposing internal complexity, INetworkStatsService calls use
general templates.  Added TelephonyManager mapping to classify network
types using broad labels like "3G" or "4G", used to drive templates.

Cleaned up Objects and Preconditions.

Change-Id: I1d4c1403f0503bc3635a59bb378841ba42239a91