Add support for ethtool -G to tune rx and tx ring sizes
per interface basis.

This is only supported for NX3031 based cards.
Signed-off-by: NAmit Kumar Salecha <amit@netxen.com>
Signed-off-by: NDhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>