Use UserHandle.USER_SYSTEM in place of 0.

Change-Id: I3bc5f2d326b0b5c6797f3ac259d0e3d42a3afa0f
diff --git a/core/java/android/net/NetworkScorerAppManager.java b/core/java/android/net/NetworkScorerAppManager.java
index a66ea49..e555fa4 100644
--- a/core/java/android/net/NetworkScorerAppManager.java
+++ b/core/java/android/net/NetworkScorerAppManager.java
@@ -93,7 +93,7 @@
     public static Collection<NetworkScorerAppData> getAllValidScorers(Context context) {
         // Network scorer apps can only run as the primary user so exit early if we're not the
         // primary user.
-        if (UserHandle.getCallingUserId() != 0 /*USER_SYSTEM*/) {
+        if (UserHandle.getCallingUserId() != UserHandle.USER_SYSTEM) {
             return Collections.emptyList();
         }