net: Zeroing the structure ethtool_wolinfo in ethtool_get_wol()

memset() the structure ethtool_wolinfo that has padded bytes
but the padded bytes have not been zeroed out.

Signed-off-by: zhanglin <zhang.lin16@zte.com.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>