ethtool: fix recursive dependency

ethtool: fix recursive dependency

Change the CONFLICTS definition from the alternative package
(ethtool-full) to the main one.

The CONFLICTS line creates a dependency to the conflicting package.

Right now, the dependency would be created in the PACKAGE_ethtool-full
symbol:

config PACKAGE_ethtool-full
        depends on m || (PACKAGE_ethtool != y)

When the main package is selected by airmon-ng, it selects
PACKAGE_ethtool, *depending* on the value of PACKAGE_ethtool-full:

config PACKAGE_airmon-ng
        select PACKAGE_ethtool if PACKAGE_ethtool-full<PACKAGE_airmon-ng

In the first block, the value of PACKAGE_ethtool-full depends on the
value of PACKAGE_ethtool.  In the second block, the opposite is true:
the value of PACKAGE_ethtool depends on the value of
PACKAGE_ethtool-full.  This is a recursive dependency.

Fix it by changing the package where the dependency is created, so that
only the value of PACKAGE_ethtool will depend on PACKAGE_ethtool-full.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>