r8169: add support for NCube 8168 network card

This card identifies itself as:
  Ethernet controller [0200]: NCube Device [10ff:8168] (rev 06)
  Subsystem: TP-LINK Technologies Co., Ltd. Device [7470:3468]

Adding a new entry to rtl8169_pci_tbl makes the card work.

Link: http://launchpad.net/bugs/1788730


Signed-off-by: Anthony Wong <anthony.wong@ubuntu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>