zebra: add hooks upon enabling / disabling a VRF

zebra_vrf_enable() is the callback for VRF_ENABLE_HOOK.
It presently needs do nothing.

zebra_vrf_disable() is the callback for VRF_DISABLE_HOOK.
It presently withdraws routes, shuts down interfaces, and
clears the router-id candidates in that VRF.

Signed-off-by: Feng Lu <lu.feng@6wind.com>
Reviewed-by: Alain Ritoux <alain.ritoux@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: Vincent JARDIN <vincent.jardin@6wind.com>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/zebra/rib.h b/zebra/rib.h
index 06aa353..5663f30 100644
--- a/zebra/rib.h
+++ b/zebra/rib.h
@@ -473,6 +473,7 @@
 extern void rib_update (vrf_id_t);
 extern void rib_weed_tables (void);
 extern void rib_sweep_route (void);
+extern void rib_close_table (struct route_table *);
 extern void rib_close (void);
 extern void rib_init (void);
 extern unsigned long rib_score_proto (u_char proto);