Make network usage on the main thread fatal (Honeycomb+)

For apps targetting Honeycomb SDK or above, make network usage on the
main thread (aka event thread, Looper thread, UI thread) be fatal.

If an app is targetting a previous SDK version, they're grandfathered
into the older (lack of) rules.

Bug: 786847
Change-Id: Ia4ae77b8369567ee526c96b930d523bc722b0bc9