net: phy: aquantia: use ADVERTISE_XNP for extended next page advertising

net: phy: aquantia: use ADVERTISE_XNP for extended next page advertising

When configuring the link parameters in forced mode for the AQR-105, the
Extended Next Page bit gets advertised for Multi-Gigabit modes.

This is done through bit 12 of MDIO_AN_ADVERTISE in MDIO_MMD_AN. This
contains a copy of the MII_ADVERTISE, for which 802.3 defines bit 12 as
the Extended Next Page advertising. This bit used to be marked as
reserved, but a proper define for it was added in :

commit e7a62edd34b1 ("net: phy: qcom: at803x: Use the correct bit to disable extended next page")

Let's use it instead of the ADVERTISE_RESV definition, making the code
more self-documenting.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20260428125827.238469-1-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>