Clear the pass oc flag bits earlier in the ban lurker

The pass bits of the oc's flags wasn't cleared before or'ing the new
pass on failing the busy object test in the ban lurker. This would
cause the pass not to be matched later, making the lurker spin on the
busy object.

Fixes: #1470

bin/varnishd/cache_ban.c

@@ -843,6 +843,10 @@ ban_lurker_work(const struct sess *sp, unsigned pass)
 				TIM_sleep(params->ban_lurker_sleep);
 				continue;
 			}
+			/*
+			 * Clear this oc's pass bits.
+			 */
+			oc->flags &= ~OC_F_LURK;
 			/*
 			 * If the object is busy, we can't touch
 			 * it. Defer it to a later run.
@@ -861,7 +865,6 @@ ban_lurker_work(const struct sess *sp, unsigned pass)
 			 */
 			AN(oc->refcnt);
 			oc->refcnt++;
-			oc->flags &= ~OC_F_LURK;
 			Lck_Unlock(&ban_mtx);
 			/*
 			 * Get the object and check it against all relevant bans