Fix SEGV in ip ospf neighbor all

Dont use vty->index in show_ip_ospf_neighbor_all_cmd(),
It is invalid, use ospf_lookup() instead.
diff --git a/ospfd/ospf_vty.c b/ospfd/ospf_vty.c
index 5307b41..11f12c5 100644
--- a/ospfd/ospf_vty.c
+++ b/ospfd/ospf_vty.c
@@ -3093,7 +3093,7 @@
        "Neighbor list\n"
        "include down status neighbor\n")
 {
-  struct ospf *ospf = vty->index;
+  struct ospf *ospf = ospf_lookup ();
   struct listnode *node;
   struct ospf_interface *oi;