Dns.GetHostEntryAsync(IPAddress.None) succeeds on macOS

[stephentoub]

await Dns.GetHostEntryAsync(IPAddress.None) throws a SocketException on Windows, but doesn't on Unix. I don't know if the right answer here is that the failing test should be made platform-specific for Windows (i.e. this is expected behavior on Unix) or whether there's a bug in the Unix implementation we need to fix so that this case also fails.

[KristinXie1]

Disabled test, reopen it.

[KristinXie1]

https://github.com/dotnet/corefx/blob/master/src/System.Net.NameResolution/tests/FunctionalTests/GetHostEntryTest.cs#L89

[stephentoub]

Updated: fails correctly on Windows and Linux, but doesn't on macOS. Looks like it's simply an OS behavior.