plugins: don't require CNI_NETNS for DEL command

This will allow to free up the IPAM allocations when the caller doesn't
have access to the network namespace anymore, e.g. due to a reboot.

pkg/skel/skel.go

@@ -69,7 +69,7 @@ func PluginMain(cmdAdd, cmdDel func(_ *CmdArgs) error) {
 			&netns,
 			reqForCmdEntry{
 				"ADD": true,
-				"DEL": true,
+				"DEL": false,
 			},
 		},
 		{

plugins/main/bridge/bridge.go

@@ -289,6 +289,10 @@ func cmdDel(args *skel.CmdArgs) error {
 		return err
 	}
 
+	if args.Netns == "" {
+		return nil
+	}
+
 	var ipn *net.IPNet
 	err = ns.WithNetNSPath(args.Netns, func(_ ns.NetNS) error {
 		var err error

plugins/main/ipvlan/ipvlan.go

@@ -152,6 +152,10 @@ func cmdDel(args *skel.CmdArgs) error {
 		return err
 	}
 
+	if args.Netns == "" {
+		return nil
+	}
+
 	return ns.WithNetNSPath(args.Netns, func(_ ns.NetNS) error {
 		return ip.DelLinkByName(args.IfName)
 	})

plugins/main/macvlan/macvlan.go

@@ -170,6 +170,10 @@ func cmdDel(args *skel.CmdArgs) error {
 		return err
 	}
 
+	if args.Netns == "" {
+		return nil
+	}
+
 	return ns.WithNetNSPath(args.Netns, func(_ ns.NetNS) error {
 		return ip.DelLinkByName(args.IfName)
 	})

plugins/main/ptp/ptp.go

@@ -199,6 +199,10 @@ func cmdDel(args *skel.CmdArgs) error {
 		return err
 	}
 
+	if args.Netns == "" {
+		return nil
+	}
+
 	var ipn *net.IPNet
 	err := ns.WithNetNSPath(args.Netns, func(_ ns.NetNS) error {
 		var err error