return proper error code in rename_netif()

<Md>  kay: can you look at rename_netif()? it returns -errno in a place,
      but I think that it may by changed by err() (at least)
<kay> Md: yeah, that doesn't look correct

udev/udev-event.c

@@ -472,8 +472,9 @@ static int rename_netif(struct udev_event *event)
 
 	sk = socket(PF_INET, SOCK_DGRAM, 0);
 	if (sk < 0) {
+		err = -errno;
 		err(event->udev, "error opening socket: %m\n");
-		return -errno;
+		return err;
 	}
 
 	memset(&ifr, 0x00, sizeof(struct ifreq));