wgengine/magicsock, controlclient, net/dns: reduce some logspam

Updates #cleanup

Change-Id: I78b0697a01e94baa33f3de474b591e616fa5e6af
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

net/dns/osconfig.go

@@ -8,6 +8,7 @@ import (
 	"errors"
 	"fmt"
 	"net/netip"
+	"strings"
 
 	"tailscale.com/types/logger"
 	"tailscale.com/util/dnsname"
@@ -65,6 +66,42 @@ type OSConfig struct {
 	MatchDomains []dnsname.FQDN
 }
 
+func (o *OSConfig) WriteToBufioWriter(w *bufio.Writer) {
+	if o == nil {
+		w.WriteString("<nil>")
+		return
+	}
+	w.WriteString("{")
+	if len(o.Hosts) > 0 {
+		fmt.Fprintf(w, "Hosts:%v ", o.Hosts)
+	}
+	if len(o.Nameservers) > 0 {
+		fmt.Fprintf(w, "Nameservers:%v ", o.Nameservers)
+	}
+	if len(o.SearchDomains) > 0 {
+		fmt.Fprintf(w, "SearchDomains:%v ", o.SearchDomains)
+	}
+	if len(o.MatchDomains) > 0 {
+		w.WriteString("SearchDomains:[")
+		sp := ""
+		var numARPA int
+		for _, s := range o.MatchDomains {
+			if strings.HasSuffix(string(s), ".arpa.") {
+				numARPA++
+				continue
+			}
+			w.WriteString(sp)
+			w.WriteString(string(s))
+			sp = " "
+		}
+		w.WriteString("]")
+		if numARPA > 0 {
+			fmt.Fprintf(w, "+%darpa", numARPA)
+		}
+	}
+	w.WriteString("}")
+}
+
 func (o OSConfig) IsZero() bool {
 	return len(o.Nameservers) == 0 && len(o.SearchDomains) == 0 && len(o.MatchDomains) == 0
 }