android: fix network change handling on API levels < 24

Fixes #12313

In case if VPN toggled on<->off `wasConnected` returns true and
`delegate.enterIdle()` is skipped.

Author: dmytroreutov

android/src/main/java/io/grpc/android/AndroidChannelBuilder.java

@@ -323,17 +323,15 @@ public void onBlockedStatusChanged(Network network, boolean blocked) {
 
     /** Respond to network changes. Only used on API levels < 24. */
     private class NetworkReceiver extends BroadcastReceiver {
-      private boolean isConnected = false;
 
       @SuppressWarnings("deprecation")
       @Override
       public void onReceive(Context context, Intent intent) {
         ConnectivityManager conn =
             (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
         android.net.NetworkInfo networkInfo = conn.getActiveNetworkInfo();
-        boolean wasConnected = isConnected;
-        isConnected = networkInfo != null && networkInfo.isConnected();
-        if (isConnected && !wasConnected) {
+
+        if (networkInfo != null && networkInfo.isConnected()) {
           delegate.enterIdle();
         }
       }

android/src/test/java/io/grpc/android/AndroidChannelBuilderTest.java

@@ -152,12 +152,6 @@ public void networkChanges_api23() {
         .sendBroadcast(new Intent(ConnectivityManager.CONNECTIVITY_ACTION));
     assertThat(delegateChannel.enterIdleCount).isEqualTo(1);
 
-    // The broadcast receiver may fire when the active network status has not actually changed
-    ApplicationProvider
-        .getApplicationContext()
-        .sendBroadcast(new Intent(ConnectivityManager.CONNECTIVITY_ACTION));
-    assertThat(delegateChannel.enterIdleCount).isEqualTo(1);
-
     // Drop the connection
     shadowOf(connectivityManager).setActiveNetworkInfo(null);
     ApplicationProvider