fix linter findings for windows and darwin

plugins/inputs/ethtool/ethtool.go

@@ -10,14 +10,6 @@ var sampleConfig string
 
 const pluginName = "ethtool"
 
-type command interface {
-	init() error
-	driverName(intf namespacedInterface) (string, error)
-	interfaces(includeNamespaces bool) ([]namespacedInterface, error)
-	stats(intf namespacedInterface) (map[string]uint64, error)
-	get(intf namespacedInterface) (map[string]uint64, error)
-}
-
 func (*Ethtool) SampleConfig() string {
 	return sampleConfig
 }

plugins/inputs/ethtool/ethtool_linux.go

@@ -57,6 +57,14 @@ type Ethtool struct {
 	command command
 }
 
+type command interface {
+	init() error
+	driverName(intf namespacedInterface) (string, error)
+	interfaces(includeNamespaces bool) ([]namespacedInterface, error)
+	stats(intf namespacedInterface) (map[string]uint64, error)
+	get(intf namespacedInterface) (map[string]uint64, error)
+}
+
 type commandEthtool struct {
 	log                 telegraf.Logger
 	namespaceGoroutines map[string]*namespaceGoroutine

plugins/inputs/ethtool/namespace_linux.go

@@ -1,3 +1,5 @@
+//go:build linux
+
 package ethtool
 
 import (
@@ -11,6 +13,19 @@ import (
 	"github.com/influxdata/telegraf"
 )
 
+type namespace interface {
+	name() string
+	interfaces() ([]namespacedInterface, error)
+	driverName(intf namespacedInterface) (string, error)
+	stats(intf namespacedInterface) (map[string]uint64, error)
+	get(intf namespacedInterface) (map[string]uint64, error)
+}
+
+type namespacedInterface struct {
+	net.Interface
+	namespace namespace
+}
+
 type namespacedAction struct {
 	result chan<- namespacedResult
 	f      func(*namespaceGoroutine) (interface{}, error)