radvd: Install and configure radvd

The *radvd* role and `radvd.yml` playbook can be used to configure the
`radvd` IPv6 SLAAC router advertisement daemon on Linux.

roles/radvd/tasks/main.yml

@@ -0,0 +1,23 @@
+- name:  ensure radvd is installed
+  package:
+    name=radvd
+    state=present
+  tags:
+  - install
+
+- name: ensure radvd is configured
+  template:
+    src=radvd.conf.j2
+    dest=/etc/radvd.conf
+    mode=0644
+  notify: restart radvd
+
+- name: ensure radvd starts at boot
+  service:
+    name=radvd
+    enabled=yes
+- meta: flush_handlers
+- name: ensure radvd is running
+  service:
+    name=radvd
+    state=started