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.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>