Serialize created listeners to disk

The created listeners are now stored to disk like created servers
are. This allows them to be used even after a restart.

Currently, the listeners cannot be deleted and need to be manually
removed.

include/maxscale/listener.h

@@ -49,6 +49,7 @@ typedef struct servlistener
     unsigned short port;        /**< Port to listen on */
     char *address;              /**< Address to listen with */
     char *authenticator;        /**< Name of authenticator */
+    char *auth_options;         /**< Authenticator options */
     void *auth_instance;        /**< Authenticator instance created in GWAUTHENTICATOR::initialize() */
     SSL_LISTENER *ssl;          /**< Structure of SSL data or NULL */
     struct dcb *listener;       /**< The DCB for the listener */
@@ -59,6 +60,18 @@ typedef struct servlistener
     struct  servlistener *next; /**< Next service protocol */
 } SERV_LISTENER;
 
+/**
+ * @brief Serialize a listener to a file
+ *
+ * This converts @c listener into an INI format file. This allows created listeners
+ * to be persisted to disk. This will replace any existing files with the same
+ * name.
+ *
+ * @param listener Listener to serialize
+ * @return True if the serialization of the listener was successful, false if it fails
+ */
+bool listener_serialize(const SERV_LISTENER *listener);
+
 SERV_LISTENER* listener_alloc(struct service* service, const char* name, const char *protocol,
                const char *address, unsigned short port, const char *authenticator,
                const char* auth_options, SSL_LISTENER *ssl);