[tests] Simplify NWPathTest.EnumerateGatewayTest (#20853)

* Remove code to test NWPath.EnumerateInterfaces, because this method is already tested elsewhere.
* Assume that if the test fails to find any gateways, it might be because the
  current machine doesn't have any (which happens on one of my machines), and
  in that case ignore the test.

tests/monotouch-test/Network/NWPathTest.cs

@@ -170,27 +170,21 @@ namespace MonoTouchFixtures.Network {
 		public void EnumerateGatewayTest ()
 		{
 			var e1 = new TaskCompletionSource<bool> ();
-			var e2 = new TaskCompletionSource<bool> ();
 			var monitor = new NWPathMonitor ();
 			try {
 				monitor.SetQueue (DispatchQueue.DefaultGlobalQueue);
-				monitor.Start ();
 				monitor.SnapshotHandler += path => {
 					path.EnumerateGateways (gateway => {
 						e1.TrySetResult (true);
 						return true;
 					});
-
-					path.EnumerateInterfaces (@interface => {
-						e2.TrySetResult (true);
-						return true;
-					});
 				};
+				monitor.Start ();
 				var rv = TestRuntime.RunAsync (TimeSpan.FromSeconds (5),
 						Task.CompletedTask,
-						Task.WhenAll (e1.Task, e2.Task));
+						e1.Task);
 				if (!rv)
-					TestRuntime.IgnoreInCI ("This test doesn't seem to be working on the bots, uncommon network setup?");
+					Assert.Ignore ("No gateways on this machine?"); // no gateways isn't all that uncommon, so just always ignore in this case.
 				Assert.IsTrue (rv, "Called back");
 			} finally {
 				monitor.Cancel ();