kni: remove ethtool support

kni: remove ethtool support

Current design requires kernel drivers and they need to be probed by
Linux up to some level so that they can be usable by DPDK for ethtool
support, this requires maintaining the Linux drivers in DPDK.

Also ethtool support is limited and hard, if not impossible, to expand
to other PMDs.

Since KNI ethtool support is not used commonly, if not used at all,
removing the support for the sake of simplicity and maintenance.

Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>