avast! is only an antivirus.
You can't allow the TCP 4662 and the UDP 4672 port, you can scan them with avast.
avast! P2P provider will scan the downloaded file.
WebShield provider scans only HTTP and not TCP and UDP protocols. Look, avast! is the only antivirus with WebShield. The other protocols, for the way of transmitting data can't be scanned. Only the file, when completed into your HDD will be.