r8169: deprecate support for RTL_GIGA_MAC_VER_27

r8169: deprecate support for RTL_GIGA_MAC_VER_27

RTL8168dp is ancient anyway, and I haven't seen any trace of its early
version 27 yet. This chip versions needs quite some special handling,
therefore it would facilitate driver maintenance if support for it
could be dropped. For now just disable detection of this chip version.
If nobody complains we can remove support for it in the near future.

v2:
- extend unknown chip version error message

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/ca98f018-a0e1-8762-e95c-f0ad773a0271@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>