Rename ratelimit_test to ratelimit_below

When I see "test", I have to think three times what the return value
means. With "below" this is immediately clear. ratelimit_below(&limit)
sounds almost like English and is imho immediately obvious.

(I also considered ratelimit_ok, but this strongly implies that being under the
limit is somehow better. Most of the times this is true, but then we use the
ratelimit to detect triple-c-a-d, and "ok" doesn't fit so well there.)

C.f. a1bcaa07.

src/core/unit.c

@@ -1695,7 +1695,7 @@ void unit_status_emit_starting_stopping_reloading(Unit *u, JobType t) {
 int unit_start_limit_test(Unit *u) {
         assert(u);
 
-        if (ratelimit_test(&u->start_limit)) {
+        if (ratelimit_below(&u->start_limit)) {
                 u->start_limit_hit = false;
                 return 0;
         }
@@ -1988,7 +1988,7 @@ static void unit_check_unneeded(Unit *u) {
         /* If stopping a unit fails continuously we might enter a stop
          * loop here, hence stop acting on the service being
          * unnecessary after a while. */
-        if (!ratelimit_test(&u->auto_stop_ratelimit)) {
+        if (!ratelimit_below(&u->auto_stop_ratelimit)) {
                 log_unit_warning(u, "Unit not needed anymore, but not stopping since we tried this too often recently.");
                 return;
         }
@@ -2038,7 +2038,7 @@ static void unit_check_binds_to(Unit *u) {
         /* If stopping a unit fails continuously we might enter a stop
          * loop here, hence stop acting on the service being
          * unnecessary after a while. */
-        if (!ratelimit_test(&u->auto_stop_ratelimit)) {
+        if (!ratelimit_below(&u->auto_stop_ratelimit)) {
                 log_unit_warning(u, "Unit is bound to inactive unit %s, but not stopping since we tried this too often recently.", other->id);
                 return;
         }