net: macb: set default_an_inband to true for SGMII

net: macb: set default_an_inband to true for SGMII

Most platforms using GEM in SGMII mode use in-band autonegotiation
because it is on by default in GEM's 1G PCS and is always on since
commit e276e5e40e92 ("net: macb: Disable PCS auto-negotiation for SGMII
fixed-link mode"). Leave it on if possible using the "default_an_inband"
flag of "struct phylink_config" so that platforms that lack in-band
autonegotiation configurability at the PHY do not break with commit
1338cfef1ff1 ("net: macb: fix SGMII with inband aneg disabled") which
will turn off in-band autoneg for non hot pluggable PHYs.

Once the majority of the PHY drivers that support SGMII have the
->config_inband() callback, this commit could be reverted so that non
hot pluggable PHY use outband negotiation with macb, like its the case
for other MACs.

Fixes: 1338cfef1ff1 ("net: macb: fix SGMII with inband aneg disabled")
Reported-by: Conor Dooley <conor.dooley@microchip.com>
Closes: https://lore.kernel.org/r/20260304-nebulizer-rounding-40fbc81a2ba1@spud
Signed-off-by: Charles Perry <charles.perry@microchip.com>
Tested-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/20260313142140.4040647-1-charles.perry@microchip.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>