zebra: maintain RTADV per VRF

This moves the global variable "rtadv" into the "struct zebra_vrf",
so that RTADV feature can work per VRF.

* rtadv.c/rtadv.h:

  Add a proper parameter to the functions so that the entity of the
  "struct zebra_vrf" and interfaces can be obtained from the specified
  VRF.

  The old rtadv_init() is splitted into:
  - rtadv_cmd_init(): it installs the RTADV commands; is called from
                      main();
  - new rtadv_init(): it creates the socket; is called from
                      zebra_vrf_enable().

  rtadv_terminate() is added to stop the threads, close the socket and
  clear the counters. It is called from zebra_vrf_disable().

  rtadv_make_socket() now calls vrf_socket() to create a socket in
  the VRF.

* interface.h and rib.h: define the macro RTADV.
* main.c: according changes, refer to rtadv.c.

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/main.c b/zebra/main.c
index 1e9757b..08cc247 100644
--- a/zebra/main.c
+++ b/zebra/main.c
@@ -229,6 +229,9 @@
 
   assert (zvrf);
 
+#ifdef RTADV
+  rtadv_init (zvrf);
+#endif
   return 0;
 }
 
@@ -253,6 +256,10 @@
         if_down (ifp);
     }
 
+#ifdef RTADV
+  rtadv_terminate (zvrf);
+#endif
+
   list_delete_all_node (zvrf->rid_all_sorted_list);
   list_delete_all_node (zvrf->rid_lo_sorted_list);
 
@@ -394,7 +401,7 @@
   access_list_init ();
   prefix_list_init ();
 #ifdef RTADV
-  rtadv_init ();
+  rtadv_cmd_init ();
 #endif
 #ifdef HAVE_IRDP
   irdp_init();