`uber-trace-id` from incoming request overwrites client span in spring cloud gateway tracing

[rafis]

Client span is generated here:

java-spring-cloud/instrument-starters/opentracing-spring-cloud-gateway-starter/src/main/java/io/opentracing/contrib/spring/cloud/gateway/TraceRequestHttpHeadersFilter.java

Lines 55 to 60 in 8a865d5

	Span span = this.tracer.buildSpan(path(builder))
	.asChildOf(tracer.activeSpan())
	.withTag(Tags.COMPONENT.getKey(), COMPONENT)
	.withTag(Tags.SPAN_KIND.getKey(), Tags.SPAN_KIND_CLIENT)
	.withTag(ROUTE_ID, getRouteId(exchange))
	.start();

Next we try to inject this span into Http Headers of inner request:

java-spring-cloud/instrument-starters/opentracing-spring-cloud-gateway-starter/src/main/java/io/opentracing/contrib/spring/cloud/gateway/TraceRequestHttpHeadersFilter.java

Lines 65 to 70 in 8a865d5

	this.tracer.inject(span.context(), Format.Builtin.HTTP_HEADERS, new HttpHeadersCarrier(headersWithInput));
	} catch (Exception ignore) {
	log.error("TraceRequestHttpHeadersFilter error", ignore);
	}
	headersWithInput.addAll(input);
	addHeadersWithInput(builder, headersWithInput);

But if the incoming request to Spring Cloud Gateway had it own uber-trace-id header this will overwrite what we just tried to do. Is it a bug?