Replace requestNetwork with registerSystemDefaultNetworkCallback

Vpn used registerSystemDefaultNetworkCallback to listen the
underlying network, so the test code should also update.

Bug: 236409954
Test: atest FrameworksNetTests
Change-Id: Ide344a1bbac9d8560fbe8addac667ff5b14a4c6f
diff --git a/tests/unit/java/com/android/server/connectivity/VpnTest.java b/tests/unit/java/com/android/server/connectivity/VpnTest.java
index 041e4ea..caef54a 100644
--- a/tests/unit/java/com/android/server/connectivity/VpnTest.java
+++ b/tests/unit/java/com/android/server/connectivity/VpnTest.java
@@ -1457,7 +1457,7 @@
         final ArgumentCaptor<NetworkCallback> networkCallbackCaptor =
                 ArgumentCaptor.forClass(NetworkCallback.class);
         verify(mConnectivityManager, timeout(TEST_TIMEOUT_MS))
-                .requestNetwork(any(), networkCallbackCaptor.capture());
+                .registerSystemDefaultNetworkCallback(networkCallbackCaptor.capture(), any());
 
         // onAvailable() will trigger onDefaultNetworkChanged(), so NetdUtils#setInterfaceUp will be
         // invoked. Set the return value of INetd#interfaceGetCfg to prevent NullPointerException.