net: sfp: extend bitrate-derived mode for 2500BASE-X

Extend the bitrate-derived support to include 2500BASE-X for modules
that report a bitrate of 2500Mbaud.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/E1kyYQf-0004iY-Gh@rmk-PC.armlinux.org.uk


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