Retry again when connection is broken

[lisongmin]

The DNS query will be dropped if the connection is lost, resulting in a DNS query timeout.
We can avoid this timeout by retrying with a new connection.

Here is the logs before this PR(testing by dig command):

Jan 25 11:01:24  sing-box[208068]: DEBUG[8693] [1845195939 0ms] dns: exchange www.baidu.com. IN A via dns-v4
Jan 25 11:01:24  sing-box[208068]: ERROR[8693] [1845195939 0ms] dns: exchange failed for www.baidu.com. IN A: NO_ERROR (remote): 168:Connection max age expired
Jan 25 11:01:29  sing-box[208068]: INFO[8698] [3587433723 0ms] inbound/direct[dns-entry]: inbound packet connection from 127.0.0.1:34366
Jan 25 11:01:29  sing-box[208068]: INFO[8698] [3587433723 0ms] inbound/direct[dns-entry]: inbound packet connection to :0
Jan 25 11:01:29  sing-box[208068]: DEBUG[8698] [3587433723 0ms] router: match[0] inbound=dns-entry => hijack-dns
Jan 25 11:01:29  sing-box[208068]: DEBUG[8698] [3587433723 0ms] router: sniffed packet protocol: dns
Jan 25 11:01:29  sing-box[208068]: DEBUG[8698] [3587433723 0ms] router: match[8] rule_set=geosite-cn => route(dns-v4)
Jan 25 11:01:29  sing-box[208068]: DEBUG[8698] [3587433723 0ms] router: match[8] => route(dns-v4)
Jan 25 11:01:29  sing-box[208068]: DEBUG[8698] [3587433723 0ms] dns: exchange www.baidu.com. IN A via dns-v4
Jan 25 11:01:29  sing-box[208068]: INFO[8698] [3587433723 0ms] outbound/trojan[proxy]: outbound multiplex packet connection to 8.8.8.8:443
Jan 25 11:01:30  sing-box[208068]: DEBUG[8699] [3587433723 622ms] dns: exchanged www.baidu.com NOERROR 13
Jan 25 11:01:30  sing-box[208068]: INFO[8699] [3587433723 622ms] dns: exchanged CNAME www.baidu.com. 13 IN CNAME www.a.shifen.com.

And the logs after apply this PR:

Jan 25 19:11:39  sing-box[620606]: DEBUG[4478] [1233815260 0ms] dns: exchange www.baidu.com. IN A via dns-v4
Jan 25 19:11:39  sing-box[620606]: DEBUG[4478] [1233815260 0ms] dns: exchange retry again for www.baidu.com. IN A failed with: NO_ERROR (remote): 168:Connection max age expired
Jan 25 19:11:39  sing-box[620606]: INFO[4478] [1233815260 0ms] outbound/trojan[proxy]: outbound multiplex packet connection to 8.8.8.8:443
Jan 25 19:11:40  sing-box[620606]: DEBUG[4479] [1233815260 609ms] dns: exchanged www.baidu.com NOERROR 12
Jan 25 19:11:40  sing-box[620606]: INFO[4479] [1233815260 609ms] dns: exchanged CNAME www.baidu.com. 12 IN CNAME www.a.shifen.com.
Jan 25 19:11:40  sing-box[620606]: INFO[4479] [1233815260 609ms] dns: exchanged CNAME www.a.shifen.com. 12 IN CNAME www.wshifen.com.
Jan 25 19:11:40  sing-box[620606]: INFO[4479] [1233815260 609ms] dns: exchanged A www.wshifen.com. 12 IN A 103.235.46.96
Jan 25 19:11:40  sing-box[620606]: INFO[4479] [1233815260 609ms] dns: exchanged A www.wshifen.com. 12 IN A 103.235.47.188