This reduces verbose assertions and makes the test more compact.
I'm not sure whether it's actually more valuable, since the
current code, while more verbose, is probably more
straightforward to understand.
Also add a test for passing in a null underlying network (i.e.,
follow default network). This requires a minor refactoring in
ConnectivityService because the applyUnderlyingCapabilities does
not currently treat null specially.
Bug: 173331190
Test: test-only change
Change-Id: Ic5a3e16969ea9e1a529706850f148cb0d5fd8e09
d7caf838c0