Show platform not supported warning only on plugin creation (#6801)

plugins/inputs/wireless/wireless.go

@@ -7,7 +7,8 @@ import (
 
 // Wireless is used to store configuration values.
 type Wireless struct {
-	HostProc string `toml:"host_proc"`
+	HostProc string          `toml:"host_proc"`
+	Log      telegraf.Logger `toml:"-"`
 }
 
 var sampleConfig = `

plugins/inputs/wireless/wireless_notlinux.go

@@ -3,19 +3,21 @@
 package wireless
 
 import (
-	"log"
-
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/plugins/inputs"
 )
 
+func (w *Wireless) Init() error {
+	w.Log.Warn("Current platform is not supported")
+	return nil
+}
+
 func (w *Wireless) Gather(acc telegraf.Accumulator) error {
 	return nil
 }
 
 func init() {
 	inputs.Add("wireless", func() telegraf.Input {
-		log.Print("W! [inputs.wireless] Current platform is not supported")
 		return &Wireless{}
 	})
 }