Update mailserver role for rmilter change

The rmilter package changed the name of its listener service similar to
what was done for rspamd (see commit 2dbc976b).

roles/mailserver/tasks/rspamd.yml

 - name: Configure rmilter
   copy: src=etc_rmilter.conf.common dest=/etc/rmilter.conf.common
 
-- name: Configure rmilter socket service
+- name: Configure rmilter service
   copy: src=lib_systemd_system_rmilter.socket dest=/lib/systemd/system/rmilter.socket
 
 - name: Start redis
   service: name=redis-server state=started
 
-- name: Start rspamd systemd socket listener
+- name: Start rspamd systemd listener
   service: name=rspamd state=started
 
-- name: Start rmilter systemd socket listener
-  service: name=rmilter.socket state=started
+- name: Start rmilter systemd listener
+  service: name=rmilter state=started