Here a suggested patch, currently a quick hack for inspection.
I forgot slap.h. Added it now. And manpage while I'm at it.
This needs an API change: Currently slapd/limits.c:limits_gets() takes the bound DN as an argument. The change needs a function which fetches the bound or examined DN from the Operation structure.
Typo, it's slapd/limits.c:limits_get()
Is it OK to just remove the DN argument and make the function static, so any existing binaries that call it won't silently get the changed API? Slapd doesn't call this function anywhere.
..it's not called anywhere _else_, that is.