This is unlikely to be committed, as it reverts an SA and code already on -RELEASE branches.
It serves, however, the purpose of a reference implementation.
The current code corresponds to the following commits (https://github.com/jlduran/freebsd-src/compare/base...jlduran:freebsd-src:ping-reference-implementation):
1. Revert 46d7b45a267b3d78c5054b210ff7b6c55bfca42b
2. Revert d9cacf605e2ac0f704e1ce76357cbfbe6cb63d52
3. Ignore alignment errors (d9cacf605e2ac0f704e1ce76357cbfbe6cb63d52 was created to fix this precisely)
4. Unskip some failing tests/fix/add some tests
5. Remove `#ifndef icmp_data guards` (these vestigial guards were only needed on <= 4.2BSD)
6. Fix alignment errors as minimally as possible (WIP)
Do not get too invested, as this revision will never land.