Define and use default request in Ikev2VpnRunner

Vpn might be included in ConnectivityService mainline module, so
it should prevent calling @hide API. Even if Vpn isn't included
in ConnectivityService mainline module eventually, it's still
fine to use local defined default request instead of calling
@hide API.
Ideally, ConnectivityManager will provide a new API which can
provide the status of physical network even though there is a
virtual network. b/147280869 is used for tracking the new API.

Bug: 172183305
Test: atest FrameworksNetTests
Test: atest CtsNetTestCasesLatestSdk
Test: Manual setup IKEV2 VPN connection.
Change-Id: If76e7497bef4890a74641695c3ebd395795bbe7f

services/core/java/com/android/server/connectivity/Vpn.java

@@ -2407,7 +2407,14 @@ public class Vpn {
                         .addTransportType(NetworkCapabilities.TRANSPORT_TEST)
                         .build();
             } else {
-                req = cm.getDefaultRequest();
+                // Basically, the request here is referring to the default request which is defined
+                // in ConnectivityService. Ideally, ConnectivityManager should provide an new API
+                // which can provide the status of physical network even though there is a virtual
+                // network. b/147280869 is used for tracking the new API.
+                // TODO: Use the new API to register default physical network.
+                req = new NetworkRequest.Builder()
+                        .addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)
+                        .build();
             }
 
             cm.requestNetwork(req, mNetworkCallback);