qualcommax: enable in-band signalling on the USXGMII ports

qualcommax: enable in-band signalling on the USXGMII ports

USXGMII carries the line rate to the MAC in a Clause 37 code word, so the
link needs in-band signalling. Without "managed" the port is PHY managed,
phylink disables in-band on the PHY, and with the PCS now honouring
neg_mode neither end runs autonegotiation, so nothing crosses the system
interface.

Every USXGMII port in this target was missing the property: ten ports
across eight boards, all of them an Aquantia PHY on copper, none of them
an SFP cage. ipq8074-rt-ax89x already carried "in-band-status" on its
SGMII lan8, which is why a file-level search made it look covered.

Only the two ports on ipq8072-301w have been tested on hardware. The
remaining eight are the same PHY family behind the same PCS, are broken
today for the same reason, and cannot regress from a state where they
pass no traffic, but they have not been confirmed on a board.

That test ran on the 6.18 testing kernel, where phylink switches the PHY
side on through phy_config_inband(). On 6.12 the PHY has no such op and
0760-net-phy-aquantia-enable-USXGMII-MAC-autoneg.patch forces the same
bit unconditionally, so the end state matches, but no board has confirmed
it there.

Tested-by: Rudy Andram <rmandrad@gmail.com>
Assisted-by: Claude:claude-opus-5
Signed-off-by: Julius Bairaktaris <julius@bairaktaris.de>
Link: https://github.com/openwrt/openwrt/pull/24420
Signed-off-by: Robert Marko <robimarko@gmail.com>