Issue title: 注释错误
 Issue body: Android的com.tencent.mars.stn.StnLogic 的533行

现在写的注释为：

```
/**
 * 网络层向上层反馈网络连接状态
 * @param status 综合状态，即长连+短连的状态
 *               kNetworkUnkown = -1, kNetworkUnavailable = 0, kGateWayFailed = 1, kServerFailed = 2, kConnecting = 3, kConnected = 4, kServerDown = 5
 * @param longlinkstatus  长连状态
 *                       kConnectIdle = 0, kConnecting = 1, kConnected, kDisConnected = 3, kConnectFailed = 4
 */
```

经过测试，感觉longlinkstatus的状态应当是错误的,应当为：
```
kConnecting = 2, kConnectFailed = 3, kConnected = 4
```

不知道我的猜测对不对。
 Comments: 
 Comment 0: 对的  这里注释写的有点问题： kConnectFailed-> kServerFailed   具体代码在[net_core.cc#L615](https://github.com/Tencent/mars/blob/master/mars/stn/src/net_core.cc#L615)
{'source': 'GithubIssues', 'repo_name_with_owner': 'Tencent/mars', 'issue_id': 209654635, 'repo_stars': 17051.0}