ethtool: add EEE_NTF notification

Send ETHTOOL_MSG_EEE_NTF notification whenever EEE settings of a network
device are modified using ETHTOOL_MSG_EEE_SET netlink message or
ETHTOOL_SEEE ioctl request.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>