http: fix format of trace information in the response header

[elek]

monkit supports http tracing information in HTTP header.

If it's properly configured, it can be enabled with sg. like this:

curl -H "tracestate: sampled=true" ...

Response will include the Trace/SpandID to make it easier to find the trace on the server side (like Jaeger).

But:

• Jaeger uses hex: might be better to switch to use hex ID
• span/trace id was swapped