Default to using the host header for request urls

See NuGet/NuGetGallery#2951

Author: maartenba

src/NuGet.Server/Web.config

@@ -50,6 +50,12 @@
     Set enableFrameworkFiltering to true to enable filtering packages by their supported frameworks during search.
     -->
     <add key="enableFrameworkFiltering" value="false" />
+    
+    <!--
+    When running NuGet.Server in a NAT network, ASP.NET may embed the erver's internal IP address in the V2 feed.
+    Uncomment the following configuration entry to enable NAT support.
+    -->
+    <!-- <add key="aspnet:UseHostHeaderForRequestUrl" value="true" /> -->
   </appSettings>
   <system.web>
     <httpRuntime maxRequestLength="31457280" />