Can't handle #[serde(tag = "someKey")] for structure while Deserialization

```
use rmp_serde::Serializer;
use serde::Serialize;

extern crate rmp_serde;
extern crate serde;
#[macro_use]
extern crate serde_derive;

#[derive(Debug, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
struct A {
b: B,
}

#[derive(Debug, Serialize, Deserialize)]
#[serde(tag = "kind", content = "data")]
#[serde(rename_all = "snake_case")]
pub enum B {
First(i32),
Second(Messagedata)
}

#[derive(Debug, Serialize, Deserialize)]
#[serde(tag = "someKey")]
pub struct Messagedata {
status: String,
message: String,
}

fn main() {
let a = A {
b: B::Second (Messagedata { status: "Failure".to_string(), message: "You are not getting the things".to_string() }),
};
//SERDE
let string_data = serde_json::to_string(&a).unwrap();
println!("data: {:?}", string_data);
let data = serde_json::from_str::(&string_data).unwrap();
println!("A: {:?}", data);
println!("-------------------------------------------------------------------------------");

//MESSAGEPACK
let mut buf = Vec::new();
a.serialize(&mut Serializer::new(&mut buf)).unwrap();
// println!("a: {:?}", buf);
let a = rmp_serde::from_slice::(&buf).unwrap();
println!("a: {:?}", a);
}

There is no problem with `serializing` and `deserializing` with `serde`. With `rmp_serde` there is no problem in `serializing` a `struct` with a given tag but while deserializing it is not able to take `tag` provided as key and giving length error.