Stay on network during ongoing traffic

Changing network might result L3 disconnection, causing
disruptive user experience.
We should change network less aggressively in the presence
of heavy traffic, which implies streaming activities.

This adds the corresponding unit tests. As a result, this
also modifies the existing test helper method |testStayOrSwitch|
and adjusts some other related unit tests.

Bug: 62428282
Test: compile, unit tests, integration tests

Change-Id: Ib285d42b7191e45e2124b2385fb0802c9fc55f71
2 files changed