my collectd setup is not pushing the logs to Logstash. Not sure what is the problem here.

I have run the tcpdump on my collectd server. Even its not sending any request. I think, the problem may be on collectd. Someone have any idea on what is wrong here.
Note : There is no block in server firewall .
I don't see anything immediately wrong with your collectd config, but try setting your Server tag to "localhost". That way you'll be sure to bind your server to your local interface.