bnx2x: Add support for ethtool -L

Add support for ethtool -L/-l for setting and getting the number of RSS queues.
The 'combined' field is used as we don't support separate IRQ for Rx and Tx.

Signed-off-by: Merav Sicron <meravs@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>