drivers: ethernet: eth_nxp_enet_qos: init phy callback in iface init

Initially phy_link_callback_set got called before iface init got set.
Moving to iface_init, fixes an issue that mac would set interface to up
even though it was down because startup phy down callback didn't got
through.

Signed-off-by: Peter van der Perk <peter.vanderperk@nxp.com>