This can be closed (please). As expected, as of upgrading to
linux-image-5.10.0-16-amd64 (= 5.10.127-1)
racoon/setkey are fine again (supposing, because of
> linux-signed-amd64 (5.10.127+1) bullseye; urgency=medium
> - Revert "net: af_key: add check for pfkey_broadcast in function
> pfkey_process"
as noted in the changelog.gz)
