iptables: do not install /etc/ethertypes

iptables: do not install /etc/ethertypes

Take inspiration from the ebtables recipe in meta-networking and omit
installation of etc/ethertypes, since it is provided by netbase. If we
don't do this, the following error occurs during build:

Error: Transaction test error:
  file /etc/ethertypes conflicts between attempted installs of
iptables-1.8.7-r0.core2_64 and netbase-1:6.3-r0.noarch

Signed-off-by: Trevor Gamblin <trevor.gamblin@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>