roles/ssh_server: missed step in ssh_lxc migration

The role was still referencing older `ansible_docker_extra_args`
variable.

Replaced with `ansible_ssh_lxc_name`.

roles/ssh_server/defaults/main.yaml

@@ -1,2 +1,2 @@
 ---
-server_fqdn: "{{ ansible_docker_extra_args or inventory_hostname }}.lilik.it"
+server_fqdn: "{{ ansible_ssh_lxc_name | default(inventory_hostname) }}.lilik.it"

roles/ssh_server/tasks/main.yaml

@@ -107,7 +107,7 @@
 
 - meta: flush_handlers
 
-- name: "waiting for ssh on {{ ansible_docker_extra_args | default(inventory_hostname) }} to start"
+- name: "waiting for ssh on {{ ansible_ssh_lxc_name | default(inventory_hostname) }} to start"
   wait_for:
     host: "{{ hostvars | ip_from_inventory(inventory_hostname) }}"
     port: 22