set_always_print_primitive_fields will serialize all oneof data.

**Describe the bug (描述bug)**
there is proto3 message
message Oneof {
oneof data {
string str1 = 1;
string str2 = 2;
}
};
message AA {
uint32 b=1;
Oneof c = 2;
}；
and aa is an response to a restful service.
And my b's right value is 0,so i use cntl->set_always_print_primitive_fields(true); to serialize b.
but i find all of c are serialized though i only set the str1 value.
中文：
因为proto3不会序列化值位default的值，所以我使用了set_always_print_primitive_fields 这个函数。但是我的message里面会有oneof类型，所以我发现所有oneof类型里面包含的都被序列化了。但是我觉得oneof类型应该只序列化我们设的值
So the json reponse is :
{
"b": 0,
"service_result": {
"str1":"xxx",
"str2":""
}
}

**To Reproduce (复现方法)**

**Expected behavior (期望行为)**
I think set_always_print_primitive_fields should not serialize oneof data

**Versions (各种版本)**
OS:centos7
Compiler:gcc11
brpc:1.3.0
protobuf:3

**Additional context/screenshots (更多上下文/截图)**

Start by reproducing the issue with the Oneof and AA messages shown, using brpc 1.3.0 and protobuf 3, then trace the implementation of set_always_print_primitive_fields. Done means primitive default fields such as b are serialized while only the active oneof field, such as str1, appears in the JSON response.

Written by the indexing model from the issue text.