Draft: USDT probing for qp operations

Currently only tracing points for dns_qp_t and dns_qpmulti_t are added. I will move on to qpcache and qpzone inside this MR if there aren't any fundamentals flaws in how this is going.

I think we can remove the GC counters completely for now. Even if the same data is going to be provided through statistics channel, it would need to switch away from global counters anyway.