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
Original-Change: https://android-review.googlesource.com/1459764
Merged-In: Ie4ee6b3c3ed7c0d414fd3cc162d4183248120895
Change-Id: Ie4ee6b3c3ed7c0d414fd3cc162d4183248120895

tests/cts/net/src/android/net/cts/CaptivePortalTest.kt

@@ -123,7 +123,7 @@ class CaptivePortalTest {
     fun testCaptivePortalIsNotDefaultNetwork() {
         assumeTrue(pm.hasSystemFeature(FEATURE_TELEPHONY))
         assumeTrue(pm.hasSystemFeature(FEATURE_WIFI))
-        utils.connectToWifi()
+        utils.ensureWifiConnected()
         utils.connectToCell()
 
         // Have network validation use a local server that serves a HTTPS error / HTTP redirect