Staging: hv: add basic ethtool support

Ethtool allows querying device information and controlling parameters.
For now just add ability to turn on/off scatter/gather.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>