r8169: re-enable MSI-X on RTL8168g

Similar to d49c88d7 ("r8169: Enable MSI-X on RTL8106e") after
e9d0ba506ea8 ("PCI: Reprogram bridge prefetch registers on resume")
we can safely assume that this also fixes the root cause of
the issue worked around by 7c53a722 ("r8169: don't use MSI-X on
RTL8168g"). So let's revert it.

Fixes: 7c53a722

 ("r8169: don't use MSI-X on RTL8168g")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>