package: ethtool: specify just one default variant

package: ethtool: specify just one default variant

Inadvertently defining 'DEFAULT_VARIANT' on both ethool and
ethtool-full variants resulted in

    $ make defconfig
    tmp/.config-package.in:121615:error: recursive dependency detected!
    tmp/.config-package.in:121615:  symbol PACKAGE_ethtool-full is selected by PACKAGE_ethtool
    tmp/.config-package.in:121605:  symbol PACKAGE_ethtool depends on PACKAGE_ethtool-full

Fix this by simply undefining 'DEFAULT_VARIANT' on the ethtool-full
variant, which is ugly, but expedient.

Fixes: https://github.com/openwrt/openwrt/commit/f4fdb996
Signed-off-by: Eric Fahlgren <ericfahlgren@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21363
Signed-off-by: Robert Marko <robimarko@gmail.com>