Do not expect broadcasts in CaptivePortalTest

The legacy broadcast may not be sent if wifi does not become the default
network within timeout. CaptivePortalTest does not need wifi to be the
default network at the start of the test, as it will be
disconnected/reconnected immediately after anyway.

Bug: 169106352
Test: atest CtsNetTestCasesLatestSdk:CaptivePortalTest
Change-Id: Ie4ee6b3c3ed7c0d414fd3cc162d4183248120895
1 file changed