vm_page_alloc_contig* don't handle VM_ALLOC_NOFREE. After commit
07297aee35f2 ("vm_page: update comments and KASSERT()s concerning page allocation"),
pmap_pdpt_allocf() triggers one of the added assertions, since pdptzone
is a NOFREE zone.
Simply clear the flag when allocating a slab. It is not worth trying to
implement support for the NOFREE allocator here.
Reported by: Jenkins