* gnu/packages/ntp.scm (openntpd)[arguments]: Add 'configure-flags to
set openntpd daemon's user and localstatedir. Add a custom phase to not
try to create said directory at install time.
* gnu/services/networking.scm (<openntpd-configuration>): New record type.
(openntpd-shepherd-service, openntpd-service-activation): New procedures.
(openntpd-service-type): New variable.
* doc/guix.texi (Networking Services): Add openntpd documentation.