Refactored NetworkManagerService to support Data Saver.

Netd provides 2 bandwidth control rules to restrict which uids can use
metered networks:

- bw_penalty_box is a blacklist-based firewall chain used to determine
  which uids do not have access to metered interfaces.

- bw_happy_box is whitelist-based firewall chain used to determine which
  uids have access to metered interfaces.

Currently, both NetworkManagerService (NMS) and
NetworkPolicyManagerService (NPMS) uses just the bw_penalty_box rule,
which makes turning Data Saver mode on / off too slow (since NPMS needs
to build the bw_penalty_box on demand); this CL adds support for both
rules on NMS, although NPMS doesn't take advantage of it yet (it will be
refactored in a separate CL).

BUG: 27127112
BUG: 26685616
Change-Id: Ib954574f7c86269fc9b4cf8ce4ba72ba5878c23d