MFC r314946:

MFC r314946:

Configure leap-second smearing (always).

Leap-second smearing is an experimental option that may be specified in
ntp.conf(5) and the -x option on the command line to spread the effect
of a leap-second over an interval as specified by the leapsmearinterval
config file statement. Recommended values are between 7200 (2 hours) and
86400 (24 hours).

It is advised that leap-second smearing not be used for public NTP
servers (https://www.meinbergglobal.com/download/burnicki/Leap\
%20Second%20Smearing%20With%20NTP.pdf). It is also advised that NTP
clients not use a mix of NTP servers using leap-second smearing with
NTP servers not using leap-second smearing as that could cause
undefined client behaviour.

Leap-second smearing was committed to ports net/ntp and net/ntp-devel
by r426825 on 2016-11-22.

Suggested by:	des

git-svn-id: svn://svn.freebsd.org/base/stable/10@316559 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f