kernel - Turn off machdep.pmap_mmu_optimize by default

kernel - Turn off machdep.pmap_mmu_optimize by default

* Turn off machdep.pmap_mmu_optimize by default.  There are some bugs that
  need to be resolved which are messing up both apache and rtorrent.

* (this feature is already turned off by default on RELEASE).

• [DBH] sys/platform/pc64/x86_64/pmap.c