kernel: rtl8261n: add post-reset MDIO stabilization delay

After the RTL8261N asserts a reset, the MDIO bus becomes temporarily
unavailable during the chip's reinitialization sequence. Any subsequent
read or write issued before the PHY has stabilized will fail.

Add a 30ms delay after triggering the reset to ensure the chip is reachable
via MDIO before resuming communication.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Link: openwrt/openwrt#23076
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

Author: jonasjelonek

target/linux/generic/files/drivers/net/phy/rtl8261n/rtk_phy.c

@@ -81,6 +81,7 @@ static int rtkphy_config_init(struct phy_device *phydev)
 
           #if 1 /* toggle reset */
             phy_modify_mmd_changed(phydev, 30, 0x145, BIT(0)  , 1);
+            mdelay(30);
             phy_modify_mmd_changed(phydev, 30, 0x145, BIT(0)  , 0);
             mdelay(30);
           #endif