[FUI03] No-op refactoring of VpnInfo

As a preparation of exposing system API. This patch does some
harmless refactoring, which includes:
  1. Move VpnInfo to android.net
  2. Add nullability annotations
  3. Make members final

Bug: 174123988
Test: TH
Change-Id: I1530bb45d0e84c28c6deac33596bc686058afc0d
diff --git a/core/java/android/net/INetworkStatsService.aidl b/core/java/android/net/INetworkStatsService.aidl
index 1a3dc97..d5aede7 100644
--- a/core/java/android/net/INetworkStatsService.aidl
+++ b/core/java/android/net/INetworkStatsService.aidl
@@ -23,11 +23,11 @@
 import android.net.NetworkStats;
 import android.net.NetworkStatsHistory;
 import android.net.NetworkTemplate;
+import android.net.VpnInfo;
 import android.net.netstats.provider.INetworkStatsProvider;
 import android.net.netstats.provider.INetworkStatsProviderCallback;
 import android.os.IBinder;
 import android.os.Messenger;
-import com.android.internal.net.VpnInfo;
 
 /** {@hide} */
 interface INetworkStatsService {
diff --git a/core/java/com/android/internal/net/VpnInfo.aidl b/core/java/android/net/VpnInfo.aidl
similarity index 94%
rename from core/java/com/android/internal/net/VpnInfo.aidl
rename to core/java/android/net/VpnInfo.aidl
index 6fc97be..8bcaa81 100644
--- a/core/java/com/android/internal/net/VpnInfo.aidl
+++ b/core/java/android/net/VpnInfo.aidl
@@ -14,6 +14,6 @@
  * limitations under the License.
  */
 
-package com.android.internal.net;
+package android.net;
 
 parcelable VpnInfo;
diff --git a/services/core/java/com/android/server/net/NetworkStatsFactory.java b/services/core/java/com/android/server/net/NetworkStatsFactory.java
index e9868fd..4faa790 100644
--- a/services/core/java/com/android/server/net/NetworkStatsFactory.java
+++ b/services/core/java/com/android/server/net/NetworkStatsFactory.java
@@ -27,6 +27,7 @@
 import android.annotation.Nullable;
 import android.net.INetd;
 import android.net.NetworkStats;
+import android.net.VpnInfo;
 import android.net.util.NetdService;
 import android.os.RemoteException;
 import android.os.StrictMode;
@@ -34,7 +35,6 @@
 
 import com.android.internal.annotations.GuardedBy;
 import com.android.internal.annotations.VisibleForTesting;
-import com.android.internal.net.VpnInfo;
 import com.android.internal.util.ArrayUtils;
 import com.android.internal.util.ProcFileReader;
 
diff --git a/services/core/java/com/android/server/net/NetworkStatsService.java b/services/core/java/com/android/server/net/NetworkStatsService.java
index 81a6641..4be7b48 100644
--- a/services/core/java/com/android/server/net/NetworkStatsService.java
+++ b/services/core/java/com/android/server/net/NetworkStatsService.java
@@ -105,6 +105,7 @@
 import android.net.NetworkTemplate;
 import android.net.TrafficStats;
 import android.net.Uri;
+import android.net.VpnInfo;
 import android.net.netstats.provider.INetworkStatsProvider;
 import android.net.netstats.provider.INetworkStatsProviderCallback;
 import android.net.netstats.provider.NetworkStatsProvider;
@@ -143,7 +144,6 @@
 
 import com.android.internal.annotations.GuardedBy;
 import com.android.internal.annotations.VisibleForTesting;
-import com.android.internal.net.VpnInfo;
 import com.android.internal.util.ArrayUtils;
 import com.android.internal.util.DumpUtils;
 import com.android.internal.util.FileRotator;