ICMP reply from every host on the internet from Smoltcp is confusing

Onionmasq effectively works as a gateway for us, but in practice it's implemented by having it respond as if all hosts on the internet is present. This means when it receives an ICMP ECHO REQUEST, it responds to it. This causes some confusion and will lead to people think we have a VPN leak.

I think we should find a way to disable the pong responses here and have it timeout. Tor doesn't support ICMP at all, so we could just drop these cells even though it has negative implications for some services.

See more info in: #115 (comment 3095818)