[System] Fix HttpListenerRequestTest.HttpRequestIsLocal intermittently failing

[System] Fix HttpListenerRequestTest.HttpRequestIsLocal intermittently failing

We're seeing the following exception on devices in CI:

```
[FAIL] HttpListenerRequestTest.HttpRequestIsLocal : System.Net.Sockets.SocketException : Could not resolve host 'XQA-AppleTV-1'
	  at System.Net.Dns.Error_11001 (System.String hostName) [0x00000] in /Users/builder/data/lanes/1381/d8287824/source/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/System/System.Net/Dns.cs:292
	  at System.Net.Dns.GetHostByName (System.String hostName) [0x00024] in /Users/builder/data/lanes/1381/d8287824/source/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/System/System.Net/Dns.cs:419
	  at System.Net.Dns.GetHostEntry (System.String hostNameOrAddress) [0x00061] in /Users/builder/data/lanes/1381/d8287824/source/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/System/System.Net/Dns.cs:380
	  at System.Net.Dns.GetHostAddresses (System.String hostNameOrAddress) [0x00065] in /Users/builder/data/lanes/1381/d8287824/source/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/System/System.Net/Dns.cs:406
	  at MonoTests.System.Net.HttpListenerRequestTest.HttpRequestIsLocal () [0x00006] in /Users/xamarinqa/QABot/data/lanes/2441/d8287824/source/xamarin-macios/external/mono/mcs/class/System/Test/System.Net/HttpListenerRequestTest.cs:197
	  at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
	  at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00038] in /Users/builder/data/lanes/1381/d8287824/source/xamarin-macios/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/corlib/System.Reflection/MonoMethod.cs:309
```

From looking at the code, resolving the hostname to IP addresses via DNS fails so the test doesn't even run.
We don't care where the local IPs come from so we can use an alternative way of getting them - via querying the network interfaces.

Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=41671

PS: fixed a hardcoded port while I was touching the code