bnx2x: Added EEE Ethtool support.

This patch extends the bnx2x's ethtool interface to enable
control in the eee feature, as well as report statistic information
about it.

Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>