Disable automatic instrumentation for zipkin exporter outbound calls (#…

…65)

Co-authored-by: Paulo Janotti <[email protected]>

src/Datadog.Trace/Agent/ZipkinApi.cs

@@ -39,6 +39,9 @@ public async Task<bool> SendTracesAsync(Span[][] traces)
                 request.Method = "POST";
                 request.ContentType = "application/json";
 
+                // Disable automatic instrumentation for Zipkin exporter
+                request.Headers.Add(HttpHeaderNames.TracingEnabled, "false");
+
                 using (var requestStream = await request.GetRequestStreamAsync().ConfigureAwait(false))
                 {
                     var serializer = new ZipkinSerializer();