macvlan cmdDel: replace the loadConf function with json.unmarshal

When the master interface on the node has deleted, and loadConf tries to
get the MTU, This causes cmdDel to return a linkNotFound error to the
runtime. The cmdDel only needs to unmarshall the net config. No need to
get the MTU. So we just replace the loadConf function with
json.unmarshal in cmdDel.

Signed-off-by: cyclinder <qifeng.guo@daocloud.io>

plugins/main/macvlan/macvlan.go

@@ -382,13 +382,13 @@ func cmdAdd(args *skel.CmdArgs) error {
 }
 
 func cmdDel(args *skel.CmdArgs) error {
-	n, _, err := loadConf(args, args.Args)
+	var n NetConf
+	err := json.Unmarshal(args.StdinData, &n)
 	if err != nil {
-		return err
+		return fmt.Errorf("failed to load netConf: %v", err)
 	}
 
 	isLayer3 := n.IPAM.Type != ""
-
 	if isLayer3 {
 		err = ipam.ExecDel(n.IPAM.Type, args.StdinData)
 		if err != nil {