Fix ConnectivityServiceTest#testNetworkCallbackMaximum

Although commit 2a84d1cbcf fixed some flakyness issues in
testNetworkCallbackMaximum so that it became stable when ran on its own,
it introduced a new source of random failures because instead of
registering callbacks after callbacks until a limit was reached, commit
2a84d1cbcf changed the test logic to push the assertions right up to
the theoretical limit.

More precisely when registering and unregistering PendingIntents in a
loop, not introducing some delay for checking that previous
PendingIntents have been effectively unregistered can cause the test to
fail. This patch fixes this issue.

Bug: 32561414
Bug: 62918393
Test: runtest frameworks-net
      testNetworkCallbackMaximum now succeeds 100 in a row on sailfish

Change-Id: I086817a738ab99fd53ba76ca8faada6151f46472

tests/net/java/com/android/server/ConnectivityServiceTest.java

@@ -3296,12 +3296,14 @@ public class ConnectivityServiceTest {
             mCm.requestNetwork(networkRequest, networkCallback);
             mCm.unregisterNetworkCallback(networkCallback);
         }
+        waitForIdle();
 
         for (int i = 0; i < MAX_REQUESTS; i++) {
             NetworkCallback networkCallback = new NetworkCallback();
             mCm.registerNetworkCallback(networkRequest, networkCallback);
             mCm.unregisterNetworkCallback(networkCallback);
         }
+        waitForIdle();
 
         for (int i = 0; i < MAX_REQUESTS; i++) {
             PendingIntent pendingIntent =
@@ -3309,6 +3311,7 @@ public class ConnectivityServiceTest {
             mCm.requestNetwork(networkRequest, pendingIntent);
             mCm.unregisterNetworkCallback(pendingIntent);
         }
+        waitForIdle();
 
         for (int i = 0; i < MAX_REQUESTS; i++) {
             PendingIntent pendingIntent =