net: phylink: set the autoneg state in phylink_phy_change

The phy_state field of phylink should carry only valid information
especially when this can be passed to the .mac_config callback.
Update the an_enabled field with the autoneg state in the
phylink_phy_change function.

Fixes: 9525ae83 ("phylink: add phylink infrastructure")
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>