Revert "usb: gadget: u_ether: Do not make UDC parent of the net device"

This reverts commit 321b5987.

This commit broke USB networking on Ingenic SoCs and maybe elsewhere.
The actual reason is unknown; and while a proper fix would be better,
we're sitting at -rc7 now, so a revert is justified - and we can work on
re-introducing this change for 6.3.

Fixes: 321b5987 ("usb: gadget: u_ether: Do not make UDC parent of the net device")
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20230209105626.10597-1-paul@crapouillou.netSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/u_ether.c

@@ -798,6 +798,7 @@ struct eth_dev *gether_setup_name(struct usb_gadget *g,
 	net->max_mtu = GETHER_MAX_MTU_SIZE;
 
 	dev->gadget = g;
+	SET_NETDEV_DEV(net, &g->dev);
 	SET_NETDEV_DEVTYPE(net, &gadget_type);
 
 	status = register_netdev(net);
@@ -872,6 +873,8 @@ int gether_register_netdev(struct net_device *net)
 	struct usb_gadget *g;
 	int status;
 
+	if (!net->dev.parent)
+		return -EINVAL;
 	dev = netdev_priv(net);
 	g = dev->gadget;
 
@@ -902,6 +905,7 @@ void gether_set_gadget(struct net_device *net, struct usb_gadget *g)
 
 	dev = netdev_priv(net);
 	dev->gadget = g;
+	SET_NETDEV_DEV(net, &g->dev);
 }
 EXPORT_SYMBOL_GPL(gether_set_gadget);