[core] Rework HEADERS PER PAGE
[core] Rework HEADERS PER PAGE

Add config variable to control how man VM pages are used per header page
Add missing field that was not subtracted off in expression for how many headers fit per header page
benohalloran/bomalloc,benohalloran/bomalloc,benohalloran/noomr,benohalloran/ipa,benohalloran/noomr,benohalloran/ipa