net: sfp: allow use 2500base-X for 2500base-T modules

Allow use of 2500base-X interface mode for PHY modules that support
2500base-T.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Daniel Machon <daniel.machon@microchip.com>
Link: https://lore.kernel.org/r/E1s15rv-00AHyk-5S@rmk-PC.armlinux.org.uk


Signed-off-by: Paolo Abeni <pabeni@redhat.com>