ospfd: use LOOKUP() for ospf_packet_type_str

* ospf_packet.h: add proper str/max extern declarations
* ospf_packet.c
  * ospf_packet_type_str: rewrite in "struct message", add max value
  * ospf_packet_add(): use LOOKUP()
  * ospf_write(): ditto
  * ospf_hello(): ditto
  * ospf_read(): ditto
* ospf_dump.h: the declaration does not belong here
* ospf_dump.c
  * ospf_header_dump(): use LOOKUP()
  * show_debugging_ospf(): ditto
diff --git a/ospfd/ospf_packet.h b/ospfd/ospf_packet.h
index 9a47208..2115f11 100644
--- a/ospfd/ospf_packet.h
+++ b/ospfd/ospf_packet.h
@@ -163,4 +163,7 @@
 extern int ospf_poll_timer (struct thread *);
 extern int ospf_hello_reply_timer (struct thread *);
 
+extern const struct message ospf_packet_type_str[];
+extern const size_t ospf_packet_type_str_max;
+
 #endif /* _ZEBRA_OSPF_PACKET_H */