Parse ICMPv6 Extended Echo (PROBE) (RFC8335)

[fenner]

Similar to #1115 for ICMP, this adds handling of ICMPv6 Extended Echo.

This spec (RFC8335) appears to be the first time where ICMP and ICMPv6 can reuse a non-trivial amount code. Therefore, this change refactors the ICMP handling into a function, and calls that function from the ICMPv6 handling.

This pattern can be reused in the future, if someone implements RFC4664/RFC5387 handling for ICMPv6, since these extensions are defined identically for ICMP and ICMPv6.

I'm willing to rebase this and the ICMP pull request to be a single pull request; I am keeping this separate for now pending feedback on this style of code reuse; if there's a long discussion to be had on that topic, then the IPv4 code can at least be merged by itself.

[fenner]

Is there something different about the linux-amd64 CI system? It can not find "icmp.h" which is part of the same change that added the #include of icmp.h. I'd like to try to fix it if I've done something wrong with my patch, but since it works on all the other systems I wonder what could be wrong.

[fxlb]

Is there something different about the linux-amd64 CI system?

Yes, it run make releasecheck to build from a release archive to see if the archive contains all the needed files. This command shows that icmp.h is missing in HDR in Makefile.in.

[fenner]

[I've updated the test outputs to match the timestamping change]

[fenner]

I've updated the v6 version to resolve conflicts with the v4 version after the merge.

[fxlb]

Thank you!

[fenner]

That's great, thank you very much!