net: pcs: rzn1-miic: update speed only if interface is changed

As stated by Russel King, miic_config() can be called as a result of
ethtool setting the configuration while the link is already up. Since
the speed is also set in this function, it could potentially modify
the current speed that is set. This will only happen if there is
no PHY present and we aren't using fixed-link mode.

Handle that by storing the current interface mode in the miic_port
structure and update the speed only if the interface mode is going to
be changed.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Link: https://lore.kernel.org/r/20220629122003.189397-1-clement.leger@bootlin.com


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