IIS integration with IPV4 only

ipv4only.cs

public static class WebHostBuilderIISExtensions
{
    private static readonly string ServerPort = "PORT";

    public static IWebHostBuilder UseIISIntegrationOnIpv4Only(this IWebHostBuilder webHostBuilder)
    {
        var port = webHostBuilder.GetSetting(ServerPort) ?? Environment.GetEnvironmentVariable($"ASPNETCORE_{ServerPort}");
        var address = "http://127.0.0.1:" + port;

        return webHostBuilder.UseIISIntegration()
                             .ConfigureServices(services =>
                             {
                                 // This is delayed until ConfigureServices since that's what UseIISIntegration does and
                                 // we need to override it
                                 webHostBuilder.UseSetting(WebHostDefaults.ServerUrlsKey, address);
                             });
    }
}