Add custom Sockopt support

[Fangliding]

#3516
虽然支持一个sockopt没有意义 但是支持自定义或许有_(吗)_
举栗

{
    "streamSettings": {
        "sockopt": {
            "customSockopt": [
                {
                "value": 114,
                "opt": 514
                },
                {
                "value": 1919,
                "opt": 810
                }
            ]
        }
    }
}

[yuhan6665]

I think it is a good idea, please make it more generic that user should be able to define level (2nd param in .Setsockopt()) as well. Also it should support different value types.. Maybe something like

message Custom {
  int64 level;
  int64 opt;
  int32 type;
  string value;
}

[Fangliding]

level是可以的 type是什么()

[Fangliding]

如果是说syscall包里的string和byte 可以这么写

{
"opt": 114,
"int": 514,
"str": "xxxx"
}

反正如果输的不正确直接在后面抛错误就行了
之前写tcp brutal的时候 因为需要直接塞二进制数据 只能golinkname把内部原始setsockopt函数导出来再用（）

[Fangliding]

改成了这样

{
"level": "6"
"opt": "114",
"int": "514",
"str": "abc"
}

支持了 value 和 int str选项 值全部改成了string 因为如果是int的话默认值是0 但是有时候一些值就是要设置为0 不知道到底是用户设置为0还是没填 所以改成字符串 检测空就是没填
level可以缺省 默认0x6即tcp

[yuhan6665]

Please keep value in one field, otherwise it is confusing what is being set. eg.

{
"level": "6"
"opt": "114",
"type": "string"/"int", // or we can do "type": 0/1, this will decide if we call SetsockoptString or SetsockoptInt. In the future we can add even more types
"value": "abc"/"1"
}

[Fangliding]

OK, it's doneee

[yuhan6665]

strconv.Atoi 的错误可能需要返回。。不过先这样吧 感谢佬！