When interface was connected to a link partner with a cable
type limitting maximum supported speed, e.g. SFP+ cable
in 25G port, driver incorrectly saved a supported speed
as the user configured speed. This prevented interface
from using all supported speeds after switching cable to SFP28.
Link was established at 10G as supported by previously used
SFP+ cable. Don't set user requested speed unless actually
configured by an user, to allow automatic selection of highest
available speed. Only when user sets custom config
using advertise_speed sysctl save it and try
to apply after cable is changed.

Also don't save initial supported speeds if FW supports
reporting default PHY config.

Signed-off-by: Krzysztof Galazka <krzysztof.galazka@intel.com>

Sponsored by: Intel Corporation