Legacy VPN calls to require a userID

This way, system applications with INTERACT_ACROSS_USERS permission will
be able to fetch the information they need.

Pre-requisite for bug 21499103

Change-Id: I7e759d5039ae6e85abc6435049016b1dcaabc834
diff --git a/services/core/java/com/android/server/ConnectivityService.java b/services/core/java/com/android/server/ConnectivityService.java
index 7f124dc..5044ba9 100644
--- a/services/core/java/com/android/server/ConnectivityService.java
+++ b/services/core/java/com/android/server/ConnectivityService.java
@@ -3112,11 +3112,11 @@
      * are checked in Vpn class.
      */
     @Override
-    public LegacyVpnInfo getLegacyVpnInfo() {
+    public LegacyVpnInfo getLegacyVpnInfo(int userId) {
+        enforceCrossUserPermission(userId);
         throwIfLockdownEnabled();
-        int user = UserHandle.getUserId(Binder.getCallingUid());
         synchronized(mVpns) {
-            return mVpns.get(user).getLegacyVpnInfo();
+            return mVpns.get(userId).getLegacyVpnInfo();
         }
     }