In vm_page_alloc_contig(), on vm_page_insert() failure, mark each
freed page as VPO_UNMANAGED. Otherwise vm_pge_free_toq() insists on
owning the page lock.

Previously, VPO_UNMANAGED was only set up to the last processed page.

Reviewed by: alc
Sponsored by: The FreeBSD Foundation
MFC after: 1 week