usbnet: asix AX88772: leave the carrier control to phylink

usbnet: asix AX88772: leave the carrier control to phylink

ASIX AX88772B based USB 10/100 Ethernet adapter doesn't come
up ("carrier off"), despite the built-in 100BASE-FX PHY positive link
indication. The internal PHY is configured (using EEPROM) in fixed
100 Mbps full duplex mode.

The primary problem appears to be using carrier_netif_{on,off}() while,
at the same time, delegating carrier management to phylink. Use only the
latter and remove "manual control" in the asix driver.

I don't have any other AX88772 board here, but the problem doesn't seem
specific to a particular board or settings - it's probably
timing-dependent.

Remove unused asix_adjust_link() as well.

Signed-off-by: Krzysztof Hałasa <khalasa@piap.pl>
Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/m3plhmdfte.fsf_-_@t19.piap.pl
Signed-off-by: Jakub Kicinski <kuba@kernel.org>