Configure leap-second smearing (always).

Leap-second smearing is an experimental option that may be specified in
ntp.conf(5) 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.

Suggested by: des