Add a skeleton VpnManagerService, and start it on boot.

This adds a lot of unused code but this should make it easier to
review subsequent CLs.

Bug: 173331190
Test: builds, boots, "dumpsys vpnmanager" succeeds
Change-Id: Ied379654a0c3ab6242d3125661fe30f322395059
diff --git a/framework/src/android/net/VpnManager.java b/framework/src/android/net/VpnManager.java
index 1e30283..a65769c 100644
--- a/framework/src/android/net/VpnManager.java
+++ b/framework/src/android/net/VpnManager.java
@@ -76,6 +76,12 @@
     @Deprecated
     public static final int TYPE_VPN_LEGACY = 3;
 
+    /**
+     * Channel for VPN notifications.
+     * @hide
+     */
+    public static final String NOTIFICATION_CHANNEL_VPN = "VPN";
+
     /** @hide */
     @IntDef(value = {TYPE_VPN_NONE, TYPE_VPN_SERVICE, TYPE_VPN_PLATFORM, TYPE_VPN_LEGACY})
     @Retention(RetentionPolicy.SOURCE)
diff --git a/services/core/java/com/android/server/connectivity/NetworkNotificationManager.java b/services/core/java/com/android/server/connectivity/NetworkNotificationManager.java
index 3d71b0a..901297c 100644
--- a/services/core/java/com/android/server/connectivity/NetworkNotificationManager.java
+++ b/services/core/java/com/android/server/connectivity/NetworkNotificationManager.java
@@ -79,7 +79,6 @@
     // server.
     public static final String NOTIFICATION_CHANNEL_NETWORK_STATUS = "NETWORK_STATUS";
     public static final String NOTIFICATION_CHANNEL_NETWORK_ALERTS = "NETWORK_ALERTS";
-    public static final String NOTIFICATION_CHANNEL_VPN = "VPN";
 
     // The context is for the current user (system server)
     private final Context mContext;