80-net-name-slot.rules: only rename network interfaces on ACTION=="add"

Otherwise systemd-udevd will rename on "change" and "move" events,
resulting in weird renames in combination with biosdevname

systemd-udevd[355]: renamed network interface eth0 to em1
systemd-udevd[355]: renamed network interface eth1 to p3p2
systemd-udevd[357]: renamed network interface eth0 to p3p1
systemd-udevd[429]: renamed network interface p3p2 to ens3f1
systemd-udevd[428]: renamed network interface p3p1 to ens3f0
systemd-udevd[426]: renamed network interface em1 to enp63s0

or

systemd-udevd[356]: renamed network interface eth0 to em1
systemd-udevd[356]: renamed network interface eth0 to p3p1
systemd-udevd[420]: renamed network interface p3p1 to ens3f0
systemd-udevd[418]: renamed network interface em1 to enp63s0
systemd-udevd[421]: renamed network interface eth1 to p3p1