driver: net: ethernet: mtk_star_emac: fix suspend/resume issue

driver: net: ethernet: mtk_star_emac: fix suspend/resume issue

Identify the cause of the suspend/resume hang: netif_carrier_off()
is called during link state changes and becomes stuck while
executing linkwatch_work().

To resolve this issue, call netif_device_detach() during the Ethernet
suspend process to temporarily detach the network device from the
kernel and prevent the suspend/resume hang.

Fixes: 8c7bd5a454ff ("net: ethernet: mtk-star-emac: new driver")
Signed-off-by: Yanqing Wang <ot_yanqing.wang@mediatek.com>
Signed-off-by: Macpaul Lin <macpaul.lin@mediatek.com>
Signed-off-by: Biao Huang <biao.huang@mediatek.com>
Link: https://patch.msgid.link/20250528075351.593068-1-macpaul.lin@mediatek.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>