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/kernel_socket.c b/zebra/kernel_socket.c
index 374ca41..fd0d8fd 100644
--- a/zebra/kernel_socket.c
+++ b/zebra/kernel_socket.c
@@ -38,6 +38,7 @@
 #include "zebra/zserv.h"
 #include "zebra/debug.h"
 #include "zebra/kernel_socket.h"
+#include "zebra/rib.h"
 
 extern struct zebra_privs_t zserv_privs;
 extern struct zebra_t zebrad;
@@ -1273,8 +1274,11 @@
 
 /* Make routing socket. */
 static void
-routing_socket (void)
+routing_socket (struct zebra_vrf *zvrf)
 {
+  if (zvrf->vrf_id != VRF_DEFAULT)
+    return;
+
   if ( zserv_privs.change (ZPRIVS_RAISE) )
     zlog_err ("routing_socket: Can't raise privileges");
 
@@ -1305,7 +1309,13 @@
 /* Exported interface function.  This function simply calls
    routing_socket (). */
 void
-kernel_init (void)
+kernel_init (struct zebra_vrf *zvrf)
 {
-  routing_socket ();
+  routing_socket (zvrf);
+}
+
+void
+kernel_terminate (struct zebra_vrf *zvrf)
+{
+  return;
 }