Answer by Dan for Android to 12.04 USB tether not working

Open the terminal (Ctrl+Alt+T) and run this command (root privileges is required):

sudo iptables -A INPUT -p tcp -d 0/0 -s 0/0 --dport 8289 -j ACCEPT

Replace 8289 with the port you want to open.

So in your case, you should use

sudo iptables -A INPUT -p tcp -d 0/0 -s 0/0 --dport 80 -j ACCEPT

This will allow all incoming and outgoing connection through port 80.

Usually, by default, this is not blocked, so if you have installed some kind of firewall, it is best to try and unblock the port using the firewall.

ref: http://www.upubuntu.com/2012/01/how-to-open-specific-port-under-ubuntu.html