Fix staticcheck linter warnings

By moving darwin specific codes to darwin file.

nameservers_darwin.go

@@ -7,6 +7,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"io"
 	"net"
 	"os/exec"
 	"regexp"
@@ -244,3 +245,38 @@ func getAllDHCPNameservers() []string {
 
 	return allNameservers
 }
+
+func patchNetIfaceName(iface *net.Interface) (bool, error) {
+	b, err := exec.Command("networksetup", "-listnetworkserviceorder").Output()
+	if err != nil {
+		return false, err
+	}
+
+	patched := false
+	if name := networkServiceName(iface.Name, bytes.NewReader(b)); name != "" {
+		patched = true
+		iface.Name = name
+	}
+	return patched, nil
+}
+
+func networkServiceName(ifaceName string, r io.Reader) string {
+	scanner := bufio.NewScanner(r)
+	prevLine := ""
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.Contains(line, "*") {
+			// Network services is disabled.
+			continue
+		}
+		if !strings.Contains(line, "Device: "+ifaceName) {
+			prevLine = line
+			continue
+		}
+		parts := strings.SplitN(prevLine, " ", 2)
+		if len(parts) == 2 {
+			return strings.TrimSpace(parts[1])
+		}
+	}
+	return ""
+}

staticdns.go

@@ -1,12 +1,8 @@
 package ctrld
 
 import (
-	"bufio"
-	"bytes"
-	"io"
 	"net"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strings"
@@ -81,38 +77,3 @@ func SavedStaticNameservers(iface *net.Interface) ([]string, string) {
 	}
 	return ns, file
 }
-
-func patchNetIfaceName(iface *net.Interface) (bool, error) {
-	b, err := exec.Command("networksetup", "-listnetworkserviceorder").Output()
-	if err != nil {
-		return false, err
-	}
-
-	patched := false
-	if name := networkServiceName(iface.Name, bytes.NewReader(b)); name != "" {
-		patched = true
-		iface.Name = name
-	}
-	return patched, nil
-}
-
-func networkServiceName(ifaceName string, r io.Reader) string {
-	scanner := bufio.NewScanner(r)
-	prevLine := ""
-	for scanner.Scan() {
-		line := scanner.Text()
-		if strings.Contains(line, "*") {
-			// Network services is disabled.
-			continue
-		}
-		if !strings.Contains(line, "Device: "+ifaceName) {
-			prevLine = line
-			continue
-		}
-		parts := strings.SplitN(prevLine, " ", 2)
-		if len(parts) == 2 {
-			return strings.TrimSpace(parts[1])
-		}
-	}
-	return ""
-}