Fix NetworkPolicy logs in dumpsys.

Right now, nothing is get logged due to an issue
with NetworkPolicyLogger.Data initialization.

Bug: 209236326
Test: adb shell dumpsys netpolicy
Change-Id: Ie0c3e3831802f317c5821676d426ff29a8bb5fa5

services/core/java/com/android/server/net/NetworkPolicyLogger.java

@@ -566,7 +566,13 @@ public class NetworkPolicyLogger {
         }
     }
 
-    private static final class Data {
+    /**
+     * Container class for all networkpolicy events data.
+     *
+     * Note: This class needs to be public for RingBuffer class to be able to create
+     * new instances of this.
+     */
+    public static final class Data {
         public int type;
         public long timeStamp;