Feature: return an ICMP REJECT when traffic is block for UDP

[bowei]

This is a nice to have:

When our policy blocks UDP traffic, it would be nice to bounce the traffic with an ICMP REJECT to give more information to the user on the disposition of their traffic.

We do need to be mindful of the behavior of this if there is a flood of UDP from the Actor if this can tickle any issues with the kernel or network packet handler that is sending the ICMP REJECT. Do we need to do some rate limiting etc?

[keithmattix]

We'll need dataplanes to implement https://datatracker.ietf.org/doc/html/draft-ietf-masque-connect-ip-13#name-tunnelling-ip-over-http. Unless we reject at atunnel which may actually be doable in a short period of time