feat: support so_reuseaddr

[zhongweikang]

1. Are you opening this pull request for bug-fixes, optimizations or new feature?

new feature

2. Please describe how these code changes achieve your intention.

支持 so_reuseaddr 可以使得 gnet 在重启过程中，不必因为 timewait 原因而导致：bind: address already in use

3. Please link to the relevant issues (if any).

#266
#272

4. Which documentation changes (if any) need to be made/updated because of this PR?

4. Checklist

• I have squashed all insignificant commits.
• I have commented my code for explaining package types, values, functions, and non-obvious lines.
• I have written unit tests and verified that all tests passes (if needed).
• I have documented feature info on the README (only when this PR is adding a new feature).
• (optional) I am willing to help maintain this change if there are issues with it later.

[panjf2000]

加一下测试。

[zhongweikang]

已经删除了 SetReuseport 中的 so_reuseaddr 部分，并新增了测试

[panjf2000]

你自己测试过了吗?

[zhongweikang]

测试过了，设置了 so_reuseaddr 时，即便处于 timewait 状态，依然可以正常启动服务（此时没有设置 so_reuseport，主从Reactor也都在正常工作）。

[panjf2000]

麻烦 rebase 一下最新的 dev 分支代码。

[zhongweikang]

Done

[panjf2000]

你这不是 rebase 啊，现在的 git log 不对，这个 PR 也不对了，你重新在我的 dev 分支上拉一个分支再修改吧。

[zhongweikang]

不好意思，那我重开一个