r8169: re-enable MSI on RTL8168c

The original change fixed an issue on RTL8168b by mimicking the vendor
driver behavior to disable MSI on chip versions before RTL8168d.
This however now caused an issue on a system with RTL8168c, see [0].
Therefore leave MSI disabled on RTL8168b, but re-enable it on RTL8168c.

[0] https://bugzilla.redhat.com/show_bug.cgi?id=1792839



Fixes: 003bd5b4 ("r8169: don't use MSI before RTL8168d")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>