Do not ignore updated services when cleaning up removed ones

When cleaning up removed services, the assumption was made that if a
service was not 'removed', it was 'clean'. In reality, it could also
be 'updated', which was then overwritten, causing services not being
restarted. Don't do that.

As a future precaution, make the dirty field const, only allowing
updates from accessor methods.

api.c

@@ -130,7 +130,7 @@ static int service_unblock(svc_t *svc)
 
 static int service_restart(svc_t *svc)
 {
-	svc->dirty = 1;
+	svc_mark_dirty(svc);
 	service_step(svc);
 	return 0;
 }