Don't dispose stream too early. (Azure#5097)

In my previous pr Azure#5035 I tried to optimize disposing of UDS. That fix was incorrect, since we rely on the fact that Stream is still open when we return `HttpResponseMessage` from `SendAsync`. Later, the consumer of `SendAsync` will dispose the `HttpResponseMessage` and it will in turn dispose the `Stream` and `Socket`.

edge-util/src/Microsoft.Azure.Devices.Edge.Util/uds/HttpUdsMessageHandler.cs

@@ -21,30 +21,30 @@ public HttpUdsMessageHandler(Uri providerUri)
         protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
         {
             var endpoint = new UnixDomainSocketEndPoint(this.providerUri.LocalPath);
-            using (Socket socket = new Socket(AddressFamily.Unix, SocketType.Stream, ProtocolType.Unspecified))
-            {
-                Events.Connecting(this.providerUri.LocalPath);
-                await socket.ConnectAsync(endpoint);
-                Events.Connected(this.providerUri.LocalPath);
-
-                using (var stream = new HttpBufferedStream(new NetworkStream(socket, true)))
-                {
-                    var serializer = new HttpRequestResponseSerializer();
-                    byte[] requestBytes = serializer.SerializeRequest(request);
 
-                    Events.SendRequest(request.RequestUri);
-                    await stream.WriteAsync(requestBytes, 0, requestBytes.Length, cancellationToken);
-                    if (request.Content != null)
-                    {
-                        await request.Content.CopyToAsync(stream);
-                    }
+            Events.Connecting(this.providerUri.LocalPath);
+            // do not dispose `Socket` or `HttpBufferedStream` here, b/c it will be used later
+            // by the consumer of HttpResponseMessage (HttpResponseMessage.Content.ReadAsStringAsync()).
+            // When HttpResponseMessage is disposed - the stream and socket is disposed as well.
+            Socket socket = new Socket(AddressFamily.Unix, SocketType.Stream, ProtocolType.Unspecified);
+            await socket.ConnectAsync(endpoint);
+            Events.Connected(this.providerUri.LocalPath);
 
-                    HttpResponseMessage response = await serializer.DeserializeResponse(stream, cancellationToken);
-                    Events.ResponseReceived(response.StatusCode);
+            var stream = new HttpBufferedStream(new NetworkStream(socket, true));
+            var serializer = new HttpRequestResponseSerializer();
+            byte[] requestBytes = serializer.SerializeRequest(request);
 
-                    return response;
-                }
+            Events.SendRequest(request.RequestUri);
+            await stream.WriteAsync(requestBytes, 0, requestBytes.Length, cancellationToken);
+            if (request.Content != null)
+            {
+                await request.Content.CopyToAsync(stream);
             }
+
+            HttpResponseMessage response = await serializer.DeserializeResponse(stream, cancellationToken);
+            Events.ResponseReceived(response.StatusCode);
+
+            return response;
         }
 
         static class Events