net/ethtool: introduce a new ioctl for per queue setting

Introduce a new ioctl ETHTOOL_PERQUEUE for per queue parameters setting.
The following patches will enable some SUB_COMMANDs for per queue
setting.

Signed-off-by: Kan Liang <kan.liang@intel.com>
Reviewed-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>