airoha: use in-band phylink for RTL8261N USXGMII ports in W1700k

airoha: use in-band phylink for RTL8261N USXGMII ports in W1700k

After the standalone Airoha PCS driver and pcs-handle binding, wan (gdm2)
and lan2 (gdm4) netdevs probe but do not pass traffic.

Similar to the Aeonsemi PHY it seems also the RTL PHY needs in-band to the
PCS for USXGMII to work correctly. This still needs to be better
investigated but in the meantime lets apply this workaround to restore
traffic.

Signed-off-by: Daniel Pawlik <pawlik.dan@gmail.com>
[ improve commit description ]
Link: https://github.com/openwrt/openwrt/pull/23383
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>