zebra, lib/memtypes.c: the netlink sockets work per VRF

This patch lets the netlink sockets work per VRF.

* The definition of "struct nlsock" is moved into zebra/rib.h.

* The previous global variables "netlink" and "netlink_cmd" now
  become the members of "struct zebra_vrf", and are initialized
  in zebra_vrf_alloc().

* All relative functions now work for a specific VRF, by adding
  a new parameter which specifies the working VRF, except those
  functions in which the VRF ID can be obtained from the interface.

* kernel_init(), interface_list() and route_read() are now also
  working per VRF, and moved from main() to zebra_vrf_enable().

* A new function kernel_terminate() is added to release the
  netlink sockets. It is called from zebra_vrf_disable().

* Correct VRF ID, instead of the previous VRF_DEFAULT, are now
  passed to the functions of processing interfaces or route
  entries.

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: Donald Sharp <sharpd@cumulusnetworks.com>
diff --git a/zebra/test_main.c b/zebra/test_main.c
index 17014ea..448d1ef 100644
--- a/zebra/test_main.c
+++ b/zebra/test_main.c
@@ -220,6 +220,9 @@
 
   assert (zvrf);
 
+  kernel_init (zvrf);
+  route_read (zvrf);
+
   return 0;
 }
 
@@ -244,6 +247,8 @@
         if_down (ifp);
     }
 
+  kernel_terminate (zvrf);
+
   return 0;
 }
 
@@ -355,8 +360,6 @@
 
   /* Make kernel routing socket. */
   zebra_vrf_init ();
-  kernel_init ();
-  route_read ();
   zebra_vty_init();
 
   /* Configuration file read*/