bgpd: implement admin distance

Until today the admin distance cannot be configured for any IPv6
routing protocol. This patch implements it for bgp.

Signed-off-by: Maitane Zotes <maz@open.ch>

patchwork #993: http://patchwork.quagga.net/patch/993/
diff --git a/bgpd/bgp_route.h b/bgpd/bgp_route.h
index c803759..8483f3d 100644
--- a/bgpd/bgp_route.h
+++ b/bgpd/bgp_route.h
@@ -227,7 +227,7 @@
 /* for bgp_nexthop and bgp_damp */
 extern void bgp_process (struct bgp *, struct bgp_node *, afi_t, safi_t);
 extern int bgp_config_write_network (struct vty *, struct bgp *, afi_t, safi_t, int *);
-extern int bgp_config_write_distance (struct vty *, struct bgp *);
+extern int bgp_config_write_distance (struct vty *, struct bgp *, afi_t, safi_t, int *);
 
 extern void bgp_aggregate_increment (struct bgp *, struct prefix *, struct bgp_info *,
 			      afi_t, safi_t);
@@ -235,6 +235,7 @@
 			      afi_t, safi_t);
 
 extern u_char bgp_distance_apply (struct prefix *, struct bgp_info *, struct bgp *);
+extern u_char ipv6_bgp_distance_apply (struct prefix *, struct bgp_info *, struct bgp *);
 
 extern afi_t bgp_node_afi (struct vty *);
 extern safi_t bgp_node_safi (struct vty *);