Replace hidden UserHandle.isApp() usage for mainline

ConnectivityService is going to become a mainline module which
is not able to access hidden APIs. NetworkPolicyManager will be
part of connectivity framework sources which should also not
access hidden APIs. Thus, replace usage of UserHandle.isApp()
by public Process.isApplicationUid() instead.

Bug: 170598012
Test: m
Change-Id: I6eecc618d574352b924cb5f33f364e2dca9d730f

core/java/android/net/NetworkPolicyManager.java

@@ -32,8 +32,8 @@ import android.content.pm.Signature;
 import android.net.wifi.WifiConfiguration;
 import android.net.wifi.WifiInfo;
 import android.os.Build;
+import android.os.Process;
 import android.os.RemoteException;
-import android.os.UserHandle;
 import android.telephony.SubscriptionPlan;
 import android.util.DebugUtils;
 import android.util.Pair;
@@ -473,7 +473,7 @@ public class NetworkPolicyManager {
     @Deprecated
     public static boolean isUidValidForPolicy(Context context, int uid) {
         // first, quick-reject non-applications
-        if (!UserHandle.isApp(uid)) {
+        if (!Process.isApplicationUid(uid)) {
             return false;
         }