net: phylink: provide fixed state for 1000base-X and 2500base-X

When decoding clause 22 state, if in-band is disabled and using either
1000base-X or 2500base-X, rather than reporting link-down, we know the
speed, and we only support full duplex. Pause modes taken from XPCS.

This fixes a problem reported by Eric Woudstra.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/E1tXGei-000EtL-Fn@rmk-PC.armlinux.org.uk


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