feat(ModemAuthentication): add pin

reach/client/protocol/v2/model/modem.go

@@ -3,12 +3,13 @@ package model
 // type : null, pap_chap, pap, chap
 // if type selected, username and password are mandatory
 type ModemAuthentication struct {
-	Authentication struct {
-		Apn      string `json:"apn"`
+	Authentication *struct {
+		Apn      string `json:"apn,omitempty"`
 		Type     string `json:"type,omitempty"`
 		Username string `json:"username,omitempty"`
 		Password string `json:"password,omitempty"`
-	} `json:"authentication"`
+	} `json:"authentication,omitempty"`
+	Pin string `json:"pin,omitempty"`
 }
 
 type ModemConfiguration struct {