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/if_sysctl.c b/zebra/if_sysctl.c
index ffa6927..bb48f61 100644
--- a/zebra/if_sysctl.c
+++ b/zebra/if_sysctl.c
@@ -30,9 +30,11 @@
 #include "ioctl.h"
 #include "log.h"
 #include "interface.h"
+#include "vrf.h"
 
 #include "zebra/rt.h"
 #include "zebra/kernel_socket.h"
+#include "zebra/rib.h"
 
 void
 ifstat_update_sysctl (void)
@@ -90,7 +92,7 @@
 
 /* Interface listing up function using sysctl(). */
 void
-interface_list ()
+interface_list (struct zebra_vrf *zvrf)
 {
   caddr_t ref, buf, end;
   size_t bufsiz;
@@ -107,6 +109,12 @@
     0 
   };
 
+  if (zvrf->vrf_id != VRF_DEFAULT)
+    {
+      zlog_warn ("interface_list: ignore VRF %u", zvrf->vrf_id);
+      return;
+    }
+
   /* Query buffer size. */
   if (sysctl (mib, MIBSIZ, NULL, &bufsiz, NULL, 0) < 0) 
     {