net: phy: realtek: Clear MDIO_AN_10GBT_CTRL_ADV10G bit

net: phy: realtek: Clear MDIO_AN_10GBT_CTRL_ADV10G bit

On RTL8127A connected to a link partner that advertises 10000baseT
speed cannot be changed to anything other than 10000baseT as 10GbE
is always advertised regardless of any setting. Fix this by
clearing MDIO_AN_10GBT_CTRL_ADV10G bit in rtl822x_config_aneg()'s
call to phy_modify_mmd_changed().

Fixes: 83d962316128 ("net: phy: realtek: add RTL8127-internal PHY")
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: Jan Klos <honza.klos@gmail.com>
Link: https://patch.msgid.link/20260620011956.37181-1-honza.klos@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>