BUG/MINOR: server: free srv.lb_nodes in free_server

lb_nodes is allocated for servers using lb_chash (balance random or
hash-type consistent).

It can be backported up to 1.8.
diff --git a/src/server.c b/src/server.c
index d8fb65a..78620e0 100644
--- a/src/server.c
+++ b/src/server.c
@@ -2197,6 +2197,7 @@
 	free(srv->curr_idle_thr);
 	free(srv->resolvers_id);
 	free(srv->addr_node.key);
+	free(srv->lb_nodes);
 
 	if (srv->use_ssl == 1 || srv->check.use_ssl == 1 || (srv->proxy->options & PR_O_TCPCHK_SSL)) {
 		if (xprt_get(XPRT_SSL) && xprt_get(XPRT_SSL)->destroy_srv)