net-misc/radvd: fix /run/radvd clobbering on systemd, bug #603106

net-misc/radvd: fix /run/radvd clobbering on systemd, bug #603106

Bug happens because systemd has two conflicting mechanisms
to create /var/run/:

Via .service file:
  RuntimeDirectory=radvd
  ProtectSystem=full

And via .tmpfilesd:
  d /run/radvd 0755 radvd radvd

Systemd end up trying to start radvd in empty /var/.

The change removes tmpfiles.d entry completely.

Instead we rely on the following mechanisms to create /run/radvd:

- openrc: /etc/init.d/radvd creates it with 'checkpath -d -o radvd:radvd ${PIDFILE%/*}'
- systemd: radvd.service creates it with 'RuntimeDirectory=radvd'

Reported-by: Randy Barlow
Bug: https://bugs.gentoo.org/603106
Package-Manager: Portage-2.3.8, Repoman-2.3.3