Unit tests for new explicitlySelected behaviour.

ag/7905088 added the ability to pass in acceptUnvalidated without
passing in explicitlySelected. Add unit tests for that code.

While I'm at it, convert a couple of "== 1"s to toBool(), and
update the comments in NetworkAgent.

Bug: 130766237
Test: atest FrameworksNetTests
Change-Id: I6b550bd621e3596975f83464c7b4b8a14269120b