MFC 221218:

MFC 221218:
Change rman_manage_region() to actually honor the rm_start and rm_end
constraints on the rman and reject attempts to manage a region that is out
of range.
- Fix various places that set rm_end incorrectly (to ~0 or ~0u instead of
  ~0ul).
- To preserve existing behavior, change rman_init() to set rm_start and
  rm_end to allow managing the full range (0 to ~0ul) if they are not set by
  the caller when rman_init() is called.

git-svn-id: svn://svn.freebsd.org/base/stable/8@223500 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f