ethernet: skip @8021x setup if configured, split teardown
We repeat the same setup of hostapd and test devices 28 times, each taking 5-7 s to complete. Let's skip teardown until we're finished with last @8021x test and let's only run set up when it's necessary - when /tmp/nm_8021x_configured file does not exist.
Skipping set up when already configured should make this change almost
transparent when single test is run using run/runtest.sh, you'd need
however to run
sh prepare/hostapd_wired.sh teardown manually
afterwards to get your test machine to clean state.
Overall speedup of ethernet feature on my test machine (el8 with NM from COPR) is around 4 minutes, from around 13 minutes to less than 9.