net: pcs: xpcs: fix C73 AN not getting enabled

[ Upstream commit c46e78ba ]

The XPCS expects clause 73 (copper backplane) autoneg to follow the
ethtool autoneg bit. It actually did that until the blamed
commit inaptly replaced state->an_enabled (coming from ethtool) with
phylink_autoneg_inband() (coming from the device tree or struct
phylink_config), as part of an unrelated phylink_pcs API conversion.

Russell King suggests that state->an_enabled from the original code was
just a proxy for the ethtool Autoneg bit, and that the correct way of
restoring the functionality is to check for this bit in the advertising
mask.

Fixes: 11059740 ("net: pcs: xpcs: convert to phylink_pcs_ops")
Link: https://lore.kernel.org/netdev/ZGNt2MFeRolKGFck@shell.armlinux.org.uk/


Suggested-by: Russell King (Oracle) <linux@armlinux.org.uk>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>