plugins/*: Don't error if the device doesn't exist

I wasn't able to test or update the dhcp plugin but from a code read it
should be fine. All the other plugins are tested and fixed

plugins/main/ipvlan/ipvlan.go

@@ -191,9 +191,18 @@ func cmdDel(args *skel.CmdArgs) error {
 		return nil
 	}
 
-	return ns.WithNetNSPath(args.Netns, func(_ ns.NetNS) error {
-		return ip.DelLinkByName(args.IfName)
+	// There is a netns so try to clean up. Delete can be called multiple times
+	// so don't return an error if the device is already removed.
+	err = ns.WithNetNSPath(args.Netns, func(_ ns.NetNS) error {
+		if _, err := ip.DelLinkByNameAddr(args.IfName, netlink.FAMILY_V4); err != nil {
+			if err != ip.ErrLinkNotFound {
+				return err
+			}
+		}
+		return nil
 	})
+
+	return err
 }
 
 func main() {