r8169: fix powering up RTL8168h

Since commit a92a0849 "r8169: improve runtime pm in general and
suspend unused ports" interfaces w/o link are runtime-suspended after
10s. On systems where drivers take longer to load this can lead to the
situation that the interface is runtime-suspended already when it's
initially brought up.
This shouldn't be a problem because rtl_open() resumes MAC/PHY.
However with at least one chip version the interface doesn't properly
come up, as reported here:
https://bugzilla.kernel.org/show_bug.cgi?id=199549

The vendor driver uses a delay to give certain chip versions some
time to resume before starting the PHY configuration. So let's do
the same. I don't know which chip versions may be affected,
therefore apply this delay always.

This patch was reported to fix the issue for RTL8168h.
I was able to reproduce the issue on an Asus H310I-Plus which also
uses a RTL8168h. Also in my case the patch fixed the issue.
Reported-by: Slava Kardakov <ojab@ojab.ru>
Tested-by: Slava Kardakov <ojab@ojab.ru>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/realtek/r8169.c

@@ -4981,6 +4981,9 @@ static void rtl_pll_power_down(struct rtl8169_private *tp)
 static void rtl_pll_power_up(struct rtl8169_private *tp)
 {
 	rtl_generic_op(tp, tp->pll_power_ops.up);
+
+	/* give MAC/PHY some time to resume */
+	msleep(20);
 }
 
 static void rtl_init_pll_power_ops(struct rtl8169_private *tp)