MX3PidAddManager submit msisdn token error?

Nobody has claimed this yet.

No any class holds `MXHTTPClient`, let it dealloc when returning, and the request cancelled without any callback.

```
- (MXHTTPOperation *)submitMsisdnTokenOtherUrl:(NSString *)url
token:(NSString*)token
medium:(NSString *)medium
clientSecret:(NSString *)clientSecret
sid:(NSString *)sid
success:(void (^)(void))success
failure:(void (^)(NSError *))failure
{
NSLog(@"[MX3PidAddManager] submitMsisdnTokenOtherUrl: %@", url);

NSDictionary *parameters = @{
@"sid": sid,
@"client_secret": clientSecret,
@"token": token
};

MXHTTPClient *httpClient = [[MXHTTPClient alloc] initWithBaseURL:nil andOnUnrecognizedCertificateBlock:nil];
return [httpClient requestWithMethod:@"POST"
path:url
parameters:parameters
success:^(NSDictionary *JSONResponse) {
success();
}
failure:failure];
}
```

Start by locating MX3PidAddManager and its submitMsisdnTokenOtherUrl: method, then inspect how MXHTTPClient request operations are retained. Verify the request lifecycle and callbacks for this method; done means the POST request remains alive long enough to complete or report failure.

Written by the indexing model from the issue text.