Track which machine the cached address list belongs to and refresh it
when ResolveRecord() advances to another machine. This keeps A/AAAA
reuse for the same machine while avoiding mixed name/address records.
Reproducer: register two machines with private addresses 10.88.1.1
and 10.88.2.1, then call io.systemd.Resolve.Hook.ResolveRecord
with both A questions in one request.
Before: the answer for the second machine used its own name but
reused the first machine's address, e.g. resolve-bug-m2 returned
10.88.1.1 instead of 10.88.2.1.
Follow-up: 3cd929f837
dongshengyuan
8a5c8b751b