Ntttcp stalling with `-P 200`

# Overview 
Ntttcp tool gets stuck in post-test cleanup in when 200(-P 200) threads are specified. 

# Repro 
Run the following commands from receiver and sender 
Receiver
 ```bash 
./src/ntttcp -D -r -m 200,*,127.0.0.1 -D -t 5
```
Sender 
```bash 
./src/ntttcp -s127.0.0.1 -P 200 -t 5`
```

Shorthand 
```bash
pip install pytest && pytest test/functional_test.py -s
```