The parameter flow control seems not strictly accurate

我设置了一条热点限流规则，qps限制设置为了10。在客户端同时开启20个线程去访问被保护的资源，得到的结果不是预期中的10个请求被接收，10个被降级，而是每次调用都会产生不同的结果，通常接收不到10个请求之后的请求就会被降级。

No source file, test, or entry point is named. Start by reproducing the hotspot flow-control rule with a QPS limit of 10 and 20 concurrent client threads, then inspect the flow-control implementation and existing tests to determine why accepted and degraded request counts vary. Done means the behavior is covered by a regression test with clearly defined accepted and degraded counts.

Written by the indexing model from the issue text.