Make mPermissionMonitor in ConnectivityService private

Since mPermissionMonitor is not used from test now.

Test: m
Change-Id: I049274023d60c8a04fccae9b6cf5cac03dd4878e

service/src/com/android/server/ConnectivityService.java

@@ -408,8 +408,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
 
     private final MockableSystemProperties mSystemProperties;
 
-    @VisibleForTesting
-    protected final PermissionMonitor mPermissionMonitor;
+    private final PermissionMonitor mPermissionMonitor;
 
     @VisibleForTesting
     final RequestInfoPerUidCounter mNetworkRequestCounter;