realtek: refactor RTL930x MAC config to fix PHY ports

realtek: refactor RTL930x MAC config to fix PHY ports

Currently, network ports using PHYs get a link, but there is no traffic.
Make it work again by moving the MAC config to phylink_mac_link_up.

A similiar change has been previously applied for RTL83xx in commit
cd958d945be0 ("realtek: 6.6: refactor mac config and link up for
RTL83xx").

Fixes: https://github.com/openwrt/openwrt/issues/17010
Signed-off-by: Jan Hoffmann <jan@3e8.eu>
Tested-by: Christoph Krapp <achterin@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/18268
Signed-off-by: Sander Vanheule <sander@svanheule.net>