netdev: fixed netdev_set_iftype

While this would issue a SET_INTERFACE to the kernel it would
not actually set netdev->type, so netdev_get_iftype would
return incorrectly.

src/netdev.c

@@ -3470,6 +3470,8 @@ int netdev_set_iftype(struct netdev *netdev, enum netdev_iftype type)
 		return -EIO;
 	}
 
+	netdev->type = type;
+
 	return 0;
 }