MFC 251470:

MFC 251470:
Do not compare the existing mask of a cpuset with a new mask when changing
the mask of a cpuset.  Also, change the cpuset's mask before updating the
masks of all children.  Previously changing a cpuset's mask first required
setting the mask to a super-set of both the old and new masks and then
changing it a second time to the new mask.

git-svn-id: svn://svn.freebsd.org/base/stable/8@252167 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f