job: start job timeout on enqueuing not when we start to process a job

This practically reverses 23e1e0c4a3.

This makes it easier to timeout individual jobs so that this timeout can
be relied on, since blocked dependencies will not influence the timeout.

src/job.c

@@ -461,8 +461,6 @@ int job_run_and_invalidate(Job *j) {
                         j->state = JOB_WAITING;
                 else if (r < 0)
                         r = job_finish_and_invalidate(j, JOB_FAILED);
-                else
-                        job_start_timer(j);
         }
 
         return r;

src/manager.c

@@ -1216,6 +1216,7 @@ static int transaction_apply(Manager *m) {
 
                 job_add_to_run_queue(j);
                 job_add_to_dbus_queue(j);
+                job_start_timer(j);
 
                 log_debug("Installed new job %s/%s as %u", j->unit->meta.id, job_type_to_string(j->type), (unsigned) j->id);
         }