Add a sysctl to allow disabling the monitoring thread.

Summary:
If a user uses powerd, or doesn't want to use the cycles monitoring, they can
now suspend the monitoring thread.

While here, reorganize the added prototypes to match existing groupings.

Reviewers: nwhitehorn, #powerpc, rpaulo

Reviewed By: #powerpc, rpaulo

Differential Revision: https://reviews.freebsd.org/D944
X-MFC-with:	r273009

MFC after:	3 weeks


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273113 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Drop support for SSLv3.

MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273114 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f