Migrate bandwidth control to NMS, omit history.

Both stats and policy make NMS calls that depend on bandwidth control
being enabled, so move enable/disable into NMS and drop calls when
disabled.  This avoids throwing heavy ISE exceptions when disabled.

Only include recent data when writing NetworkStatsHistory as part of
dumpsys call.  Introduce manual poll event for Settings UI.

Bug: 4982115, 4770435, 4515856
Change-Id: I257820b057af2f0f99c736fb4f61e55b9fdc3e66