ssh: add parameter to specify ListenAddress directives in sshd config

If no ListenAddress directives are specified, then sshd will list for
incoming connections at all addresses. You can alter this by specifying
the listen_addresses parameter. For example:
listen_addresses => '192.168.1.1,192.168.2.1'

manifests/ssh/config/sshd.pp

 # Create the sshd configuration.
 
+# listen_addresses: If you want to restrict the ssh service to listen only at
+# certain addresses, specify with this parameter. Enter them as a
+# comma-delimited list.
+#
+# Examples:
+# listen_addresses => '192.168.1.1,192.168.2.1'
+# listen_addresses => '192.168.1.1:22,192.168.2.1'
+#
+# See the sshd_config man page for what constitutes valid entries.
+#
+# If list_addresses is omitted, then the ListenAddress directive will be
+# omitted from the sshd configuration file (which is equivalent to having
+# sshd listen at _all_ addresses).
+
+
 define base::ssh::config::sshd(
-  $ensure    = 'present',
-  $gitolite  = false,
-  $hostbased = false,
-  $pubkey    = false,
-  $source    = undef,
-  $max_tries = 5,
+  $ensure           = 'present',
+  $gitolite         = false,
+  $hostbased        = false,
+  $pubkey           = false,
+  $source           = undef,
+  $max_tries        = 5,
+  $listen_addresses = 'all',
 ) {
   if $source {
     $template = undef

templates/ssh/sshd_config.erb

@@ -79,3 +79,14 @@ Subsystem sftp /usr/lib/openssh/sftp-server
 Match User gitolite
     ForceCommand /usr/share/gitolite/gitolite-wrapper
 <% end -%>
+<%
+  if (listen_addresses != 'all')
+    # Split the addresses at the commas.
+    addresses = listen_addresses.split(',')
+    addresses.each |address| do
+-%>
+ListenAddress <%= address %>
+<%
+    end
+  end
+-%>