resolved: pahole optimization for DnsQuery

Change from the last three commits:

/* size: 312, cachelines: 5, members: 46 */
/* sum members: 296, holes: 5, sum holes: 16 */
   ↓
/* size: 288, cachelines: 5, members: 46 */
/* sum members: 286, holes: 1, sum holes: 1 */

It's not a big difference, but we might have quite a few queries in flight,
so let' make this a bit more efficient.