core: move start ratelimiting check after condition checks
With #2564 unit start rate limiting was moved from after the condition checks
are to before they are made, in an attempt to fix #2467. This however resulted
in #2684. However, with a previous commit a concept of per socket unit trigger
rate limiting has been added, to fix #2467 more comprehensively, hence the
start limit can be moved after the condition checks again, thus fixing #2684.