You can perform basic packet-level filtering using Pion's SnifferReactor.  Double-click on your SnifferReactor to open the configuration dialog, and click on the "Filters" column in the "Captures" section.  By default this is set to something like "tcp port 80" -- change it to "tcp port 80 and host IP" where "IP" is the IP address of your web server (i.e. "tcp port 80 and host 208.78.25.168").  This will ignore any traffic that is not going to or from port 80 on your web server.  Note that this feature supports the full range of the Berkeley Packet Filter syntax, which is quite flexible and powerful.