BUILD: address a few remaining calloc(size, n) cases

BUILD: address a few remaining calloc(size, n) cases

In issue #2427 Ilya reports that gcc-14 rightfully complains about
sizeof() being placed in the left term of calloc(). There's no impact
but it's a bad pattern that gets copy-pasted over time. Let's fix the
few remaining occurrences (debug.c, halog, udp-perturb).

This can be backported to all branches, and the irrelevant parts dropped.