net: asix: fix "can't send until first packet is send" issue

If cable is attached after probe sequence, the usbnet framework would
not automatically start processing RX packets except at least one
packet was transmitted.

On systems with any kind of address auto configuration this issue was
not detected, because some packets are send immediately after link state
is changed to "running".

With this patch we will notify usbnet about link status change provided by the
PHYlib.

Fixes: e532a096

 ("net: usb: asix: ax88772: add phylib support")
Reported-by: Anton Lundin <glance@acc.umu.se>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Tested-by: Anton Lundin <glance@acc.umu.se>
Link: https://lore.kernel.org/r/20220624075139.3139300-1-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>