netxen: enable rss for NX2031

Enable multiple rx rings for older NX2031 chip, firmware 3.4.336
or newer supports this feature.

Signed-off-by: Amit Kumar Salecha <amit@netxen.com>
Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: David S. Miller <davem@davemloft.net>