Fix rmilter to use tcp socket

Use a Unix socket instead of a TCP socket as a Unix socket doesn't play nicely with postfix running
smtpd in a chroot. The author of rmilter recommends using a TCP socket per
https://github.com/vstakhov/rmilter/issues/39

roles/mailserver/tasks/rspamd.yml

   tags:
     - dependencies
 
-- name: Configure rmilter
+- name: Configure rmilter.common
   copy: src=etc_rmilter.conf.common dest=/etc/rmilter.conf.common
 
+- name: Configure rmilter socket
+  lineinfile: dest=/etc/rmilter.conf regexp=^bind_socket line="bind_socket = inet:9900@localhost"
+
 - name: Configure rmilter service
   copy: src=lib_systemd_system_rmilter.socket dest=/lib/systemd/system/rmilter.socket