Fix references to socket APIs, and target the lowest net standard versions possible

src/Microsoft.AspNetCore.NodeServices/HostingModels/PhysicalConnections/NamedPipeConnection.cs

@@ -9,12 +9,18 @@ namespace Microsoft.AspNetCore.NodeServices.HostingModels.PhysicalConnections
         private bool _disposedValue = false;
         private NamedPipeClientStream _namedPipeClientStream;
 
+#pragma warning disable 1998 // Because in the NET451 code path, there's nothing to await
         public override async Task<Stream> Open(string address)
         {
             _namedPipeClientStream = new NamedPipeClientStream(".", address, PipeDirection.InOut);
+#if NET451
+            _namedPipeClientStream.Connect();
+#else
             await _namedPipeClientStream.ConnectAsync().ConfigureAwait(false);
+#endif
             return _namedPipeClientStream;
         }
+#pragma warning restore 1998
 
         public override void Dispose()
         {