Ethtool_opts: fix retrieval from configwriter.

getEthtoolOpts was incorrectly defined at the configurator class
level but used for ifcfg from the ConfigWriter class (accessing
self). This patch moves it to be a module level function and
imports it from both places it is used (ifcfg and iproute2
configurators).

Change-Id: Iac6646bbad8c7431ec1c035ebc01f0180a8338ee
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/23792
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>