End netty client span before callbacks

[trask]

netty 3.8 already ends client span before callbacks:

opentelemetry-java-instrumentation/instrumentation/netty/netty-3.8/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/netty/v3_8/client/HttpClientResponseTracingHandler.java

Lines 33 to 46 in b17f20c

	if (msg.getMessage() instanceof HttpResponse) {
	instrumenter()
	.end(
	requestAndContexts.context(),
	requestAndContexts.request(),
	(HttpResponse) msg.getMessage(),
	NettyErrorHolder.getOrDefault(requestAndContexts.context(), null));
	requestContextsField.set(ctx.getChannel(), null);
	}
	// We want the callback in the scope of the parent, not the client span
	try (Scope ignored = requestAndContexts.parentContext().makeCurrent()) {
	ctx.sendUpstream(msg);
	}