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/rtread_getmsg.c b/zebra/rtread_getmsg.c
index 83ef648..7fb916f 100644
--- a/zebra/rtread_getmsg.c
+++ b/zebra/rtread_getmsg.c
@@ -96,7 +96,7 @@
 }
 
 void
-route_read (void)
+route_read (struct zebra_vrf *zvrf)
 {
 	char 			storage[RT_BUFSIZ];
 
@@ -111,6 +111,10 @@
 	struct strbuf		msgdata;
 	int			flags, dev, retval, process;
 
+	if (zvrf->vrf_id != VRF_DEFAULT) {
+		return;
+	}
+
 	if ((dev = open (_PATH_GETMSG_ROUTE, O_RDWR)) == -1) {
 		zlog_warn ("can't open %s: %s", _PATH_GETMSG_ROUTE,
 			safe_strerror (errno));