networking fixes for f25
* removes the extra ens3 ifcfg that seems to be added
by dracut at some point (cloud base did this in their
ks a year ago in c509863)
* adds net.ifnames=0 to the bootloader line, because
that seems to be necessary to actually disable consistent
device naming
* enables the network service
see https://pagure.io/atomic-wg/issue/174
(cherry picked from commit 5d987e82b3cbe6b6d53871b0652e291ceb1f7e86)