We want to use this by "shared/nm-platform", which should have
no dependency on "libnm-core".
Move "libnm-core/nm-ethtool-utils.h" to "libnm/nm-ethtool-utils.h" so
that it is only used by libnm. This file contains the defines for
the option names.
Also, symlink "libnm/nm-ethtool-utils.h" as "shared/nm-base/nm-ethtool-utils-base.h".
We want to use the same defines also internally. Since they are both
public API (must be in libnm) and should be in "shared/nm-base", this
is the way.
