cmd/cli: set DNS last when running ctrld service

On low resources Windows Server VM, profiling shows the bottle neck when
interacting with Windows DNS server to add/remove forwarders using by
calling external powershell commands. This happens because ctrld try
setting DNS before it runs.

However, it would be better if ctrld only sets DNS after all its
listeners ready. So it won't block ctrld from receiving requests.

With this change, self-check process on dual Core Windows server VM now
runs constantly fast, ~2-4 seconds when running multiple times in a row.

cmd/cli/prog.go

@@ -194,9 +194,6 @@ func (p *prog) runWait() {
 }
 
 func (p *prog) preRun() {
-	if !service.Interactive() {
-		p.setDNS()
-	}
 	if runtime.GOOS == "darwin" {
 		p.onStopped = append(p.onStopped, func() {
 			if !service.Interactive() {
@@ -206,6 +203,12 @@ func (p *prog) preRun() {
 	}
 }
 
+func (p *prog) postRun() {
+	if !service.Interactive() {
+		p.setDNS()
+	}
+}
+
 func (p *prog) setupUpstream(cfg *ctrld.Config) {
 	localUpstreams := make([]string, 0, len(cfg.Upstream))
 	ptrNameservers := make([]string, 0, len(cfg.Upstream))
@@ -388,6 +391,7 @@ func (p *prog) run(reload bool, reloadCh chan struct{}) {
 		if p.logConn != nil {
 			_ = p.logConn.Close()
 		}
+		p.postRun()
 	}
 	wg.Wait()
 }