net: phylink: add phylink_sfp_select_interface_speed()

Add phylink_sfp_select_interface_speed() which attempts to select the
SFP interface based on the ethtool speed when autoneg is turned off.
This allows users to turn off autoneg for SFPs that support multiple
interface modes, and have an appropriate interface mode selected.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/E1uWu14-005KXo-IO@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>