macvlan cmdDel: replace the loadConf function with json.unmarshal

When the master interface on the node has been deleted, and loadConf tries
to get the MTU, This causes cmdDel to return a linkNotFound error to the
runtime. The cmdDel only needs to unmarshal the netConf. No need to
get the MTU. So we just replaced 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 {