Add ACTION_VPN_MANAGER_EVENT in ConstantsShim

Before T, there is no ACTION_VPN_MANAGER_EVENT in VpnManager,
so add ACTION_VPN_MANAGER_EVENT in ConstantsShim for passing
sc-mainline-prod build.

Bug: 225010642
Test: atest FrameworksNetTests
Change-Id: I61e6ce31bc80d1a18be020d0ae0b683c3eaf4679
(cherry picked from commit 91eda06d7968d80155d25cf5e6597cdc479a2ddc)
Merged-In: I61e6ce31bc80d1a18be020d0ae0b683c3eaf4679
diff --git a/apishim/29/com/android/networkstack/apishim/api29/ConstantsShim.java b/apishim/29/com/android/networkstack/apishim/api29/ConstantsShim.java
index 7159cea..0dcd0db 100644
--- a/apishim/29/com/android/networkstack/apishim/api29/ConstantsShim.java
+++ b/apishim/29/com/android/networkstack/apishim/api29/ConstantsShim.java
@@ -40,6 +40,8 @@
     public static final int VPN_PROFILE_STATE_CONNECTING = 1;
     public static final int VPN_PROFILE_STATE_CONNECTED = 2;
 
+    public static final String ACTION_VPN_MANAGER_EVENT = "android.net.action.VPN_MANAGER_EVENT";
+
     // Constants defined in android.net.ConnectivityDiagnosticsManager.
     public static final int DETECTION_METHOD_DNS_EVENTS = 1;
     public static final int DETECTION_METHOD_TCP_METRICS = 2;