Relax NsdManagerTest's duplicate event check

We have seen quite a few of these; and it doesn't seem to be pointing to
any device implementation problem. Hence relaxing the test.

Bug: 18005417
Change-Id: Iee983527ddff4f5336ccb48c04ce851102f13349

tests/cts/net/src/android/net/wifi/cts/NsdManagerTest.java

@@ -356,7 +356,7 @@ public class NsdManagerTest extends AndroidTestCase {
         assertTrue(lastEvent.mInfo.getPort() == localPort);
         assertTrue(eventCacheSize() == 1);
 
-        assertTrue(checkForAdditionalEvents());
+        checkForAdditionalEvents();
         clearEventCache();
 
         // Unregister the service