Don't create a netdev for phy which are already attached to a netdev.
This replace kernel errors:
(null): PHY already attached
phy attach failed 4 with err -16
With:
Phy on addr 0x4 is already attached. Not creating a phy device for it.
export_netdevs will export a net device for every port. These netdev represent a port
with out traffic.
When such a device is broght down via ifconfig the port is shutdown and
vice versa. Carrier sense is working too and ethtool can be used to
control advertise, autoneg, ...