Mock Vpn.setUnderlyingNetworks()

Override Vpn.setUnderlyingNetworks() to do a direct call on the
network agent instead of relying on the Vpn class.

Bug: 230548427
Test: atest FrameworksNetTests
Change-Id: Ib7883f8a81a22317616cae79ce57a30afdd2bed4

tests/unit/java/com/android/server/ConnectivityServiceTest.java

@@ -1716,6 +1716,14 @@ public class ConnectivityServiceTest {
                 UnderlyingNetworkInfo underlyingNetworkInfo) {
             mUnderlyingNetworkInfo = underlyingNetworkInfo;
         }
+
+        @Override
+        public synchronized boolean setUnderlyingNetworks(@Nullable Network[] networks) {
+            if (!mAgentRegistered) return false;
+            mMockNetworkAgent.setUnderlyingNetworks(
+                    (networks == null) ? null : Arrays.asList(networks));
+            return true;
+        }
     }
 
     private UidRangeParcel[] toUidRangeStableParcels(final @NonNull Set<UidRange> ranges) {