Support disabling addr to hostname lookups

[kode54]

I am finding that depending on the connection, it can take 8-10 seconds before the daemon reads and responds to a query, if it sits there poking the reverse DNS with https://github.com/janikrabe/oidentd/blob/3226029233be270955c71463f48939255622e30d/src/inet_util.c#L284

If I could disable this at runtime, I would.

(I am using a layered DNS setup: AdGuard Home -> unbound, or -> dnsmasq for local addresses.)

[kode54]

Yeah, something that would disable this block of code and only print the IP address:

https://github.com/janikrabe/oidentd/blob/3226029233be270955c71463f48939255622e30d/src/oidentd.c#L263-L266