It sounds like your router forwards incoming traffic to your PC on local ports 445/135 (see NAT info, that's why you see router's IP in the pop-up). Your computer may be vulnerable (I don't say it is!!) that's why avast scans all incoming traffic on 445/135 local ports. If you don't have those ports opened or they're blocked in your firewall.. it's good for you, but avast doesn't know that.
Probably some other PCs send DCOM/LSASS exploits on your IP address and because your router doesn't block them, avast is able to scan those packets. Just turn firewall on in your router's settings - or block DCOM service in its settings.