net: wangxun: add ethtool_ops for msglevel

Add support to get and set msglevel for driver txgbe and ngbe.

Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>