Some r8168 NICs stop working upon system resume:

[  688.051096] r8169 0000:02:00.1 enp2s0f1: rtl_ep_ocp_read_cond == 0 (loop: 10, delay: 10000).
[  688.175131] r8169 0000:02:00.1 enp2s0f1: Link is Down
...
[  691.534611] r8169 0000:02:00.1 enp2s0f1: PCI error (cmd = 0x0407, status_errs = 0x0000)

Not sure if it's related, but those NICs have a BMC device at function
0:
02:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. Realtek RealManage BMC [10ec:816e] (rev 1a)

Trial and error shows that increase the loop wait on
rtl_ep_ocp_read_cond to 30 can eliminate the issue, so let
rtl8168ep_driver_start() to wait a bit longer.

Fixes: e6d6ca6e ("r8169: Add support for another RTL8168FP")
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Reviewed-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>