Only warn user of --local-addr is provided explicitly by user

[phillip-stephens]

When there is a --name-server (either explicitly provided by user or implicit from /etc/resolv.conf) that cannot be reached by the --local-addr, we'll attempt to correct the local-addr to reach the nameserver.

In the fix in #481, I made this a warn msg to the user.

However, this means the user is getting a warn whenever the --local-addr is overridden, even if it's just a default being overridden.

We'll move to erroring out if the user supplies a --local-addr we can't use, and no warn otherwise

main

~/zdns on  main! ⌚ 13:11:30
$ go run . A example.com --iterative
WARN[0000] none of the user-supplied local addresses could connect to name server 170.247.170.2:53, using local address 192.168.1.173 
WARN[0000] none of the user-supplied local addresses could connect to name server [2001:500:2::c]:53, using local address 2600:1700:1d81:2250:91de:7de9:e0fc:9acf 
{"name":"example.com","results":{"A":{"data":{"answers":[{"answer":"93.184.215.14","class":"IN","name":"example.com","ttl":3600,"type":"A"}],"protocol":"udp","resolver":"199.43.135.53:53"},"duration":0.464350583,"status":"NOERROR","timestamp":"2024-12-19T13:11:41-05:00"}}}
00h:00m:01s; 1 names scanned; 1.00 names/sec; 100.0% success rate; NOERROR: 1
00h:00m:01s; Scan Complete; 1 names scanned; 0.68 names/sec; 100.0% success rate; NOERROR: 1

This PR - only warn if user directly supplied a local-addr and we override it.

No --local-addr

$ go run . A prstephens.com --verbosity=3
{"name":"prstephens.com","results":{"A":{"data":{"additionals":[{"flags":"","type":"EDNS0","udpsize":1232,"version":0}],"answers":[{"answer":"104.21.96.65","class":"IN","name":"prstephens.com","ttl":300,"type":"A"},{"answer":"172.67.173.251","class":"IN","name":"prstephens.com","ttl":300,"type":"A"}],"protocol":"udp","resolver":"1.1.1.1:53"},"duration":0.024726667,"status":"NOERROR","timestamp":"2024-12-19T15:55:59-05:00"}}}
00h:00m:00s; Scan Complete; 1 names scanned; 39.13 names/sec; 100.0% success rate; NOERROR: 1

Supplying a --local-addr that we must override

$ go run . A prstephens.com --verbosity=3 --local-addr=127.0.0.1
FATA[0000] none of the user-supplied local addresses ([127.0.0.1]) could connect to name server 1.1.1.1:53 
exit status 1