CTS: Only listen to wifi events when toggling wifi

When counting all connectivity changed events, we were failing
on devices with sim cards because we were counting both wifi and
mobile connectivity changes the same. Since the test only
toggles wifi, changing the listener only to pay attention to wifi
changes.

Bug: 29346253
Change-Id: I1ed3b976bc21419218c780d4afc4a5e73f128496
3 files changed