bgpd: more SAFI fixes

(with resolved conflict in bgpd/bgp_packet.c)

Two macros resolving to the same integer constant broke a case block and
a more thorough merge of BGP_SAFI_VPNV4 and BGP_SAFI_VPNV6 was
performed.

* bgpd.h: MPLS-labeled VPN SAFI is AFI-independent, switch to single
* macro
* bgp_capability_test.c: update test data
* bgp_mp_attr_test.c: idem
* bgp_route.c: (bgp_maximum_prefix_overflow, bgp_table_stats_vty) update
  macro and check conditions (where appropriate)
* bgp_packet.c: (bgp_route_refresh_send, bgp_capability_send,
  bgp_update_receive, bgp_route_refresh_receive): idem
* bgp_open.c: (bgp_capability_vty_out, bgp_afi_safi_valid_indices,
  bgp_open_capability_orf, bgp_open_capability): idem
* bgp_attr.c: (bgp_mp_reach_parse, bgp_packet_attribute,
  bgp_packet_withdraw): idem
diff --git a/bgpd/bgpd.h b/bgpd/bgpd.h
index f396f72..892e7de 100644
--- a/bgpd/bgpd.h
+++ b/bgpd/bgpd.h
@@ -727,9 +727,8 @@
 #define BGP_DEFAULT_RESTART_TIME               120
 #define BGP_DEFAULT_STALEPATH_TIME             360
 
-/* SAFI which used in open capability negotiation.  */
-#define BGP_SAFI_VPNV4                         128
-#define BGP_SAFI_VPNV6                         128
+/* RFC4364 */
+#define SAFI_MPLS_LABELED_VPN                  128
 
 /* Max TTL value.  */
 #define TTL_MAX                                255