Added kernel support in EEE Ethtool commands

This patch extends the kernel's ethtool interface by adding support
for 2 new EEE commands - get_eee and set_eee.

Thanks goes to Giuseppe Cavallaro for his original patch adding this support.

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