testsuite-71: reset startlimit counter manually

testsuite-71: reset startlimit counter manually

The test cases will call quite a lot of "systemctl stop
systemd-hostnamed", hence let's make sure we reset the start limit
counter each time, to not make this eventually fail.

(At other places we disabled the start limit counter, but here I opted
for resetting it manually via 'systemctl reset-failed', to test another
facet of the mechanism)