add default firewall_ports to docker role

roles/docker/defaults/main.yml

@@ -7,6 +7,8 @@ container_gid: 1001
 
 containers: []
 
+firewall_ports: []
+
 # needs a valid systemd timer calendar event expression:
 # https://www.freedesktop.org/software/systemd/man/systemd.timer.html#OnCalendar=
 docker_pull_timer: weekly