Don't reevaluate disconnected networks

This serves no purpose and adds several log messages every time a
network disconnects.  The extra log messages contribute to
NetworkMonitor's chatty-ness and towards it getting muted.

Bug:21480101
Change-Id: I372f9939c534f77b052a15fdb2cd5288d19ddbab

services/core/java/com/android/server/ConnectivityService.java

@@ -2684,7 +2684,10 @@ public class ConnectivityService extends IConnectivityManager.Stub
         } else {
             nai = getNetworkAgentInfoForNetwork(network);
         }
-        if (nai == null) return;
+        if (nai == null || nai.networkInfo.getState() == NetworkInfo.State.DISCONNECTING ||
+            nai.networkInfo.getState() == NetworkInfo.State.DISCONNECTED) {
+            return;
+        }
         // Revalidate if the app report does not match our current validated state.
         if (hasConnectivity == nai.lastValidated) return;
         final int uid = Binder.getCallingUid();