Add lockdownEnabled parameter to always-on VPN API

Allows callers to opt-out of blockading network traffic during boot and
on VPN app failure.

Bug: 26694104
Change-Id: Ibfbd43ad09a25f2e38053fcd6306df3711f8bde2

services/core/java/com/android/server/ConnectivityService.java

@@ -3309,7 +3309,7 @@ public class ConnectivityService extends IConnectivityManager.Stub
     }
 
     @Override
-    public boolean setAlwaysOnVpnPackage(int userId, String packageName) {
+    public boolean setAlwaysOnVpnPackage(int userId, String packageName, boolean lockdown) {
         enforceConnectivityInternalPermission();
         enforceCrossUserPermission(userId);