vlib: add VLIB_NUM_WORKERS_CHANGE_FN() handler

Allows features to update their data structures after change in number
of worker threads.

Type: improvement
Change-Id: Icd4d197e28608f5bbb1edd13eb624cd98e33cafe
Signed-off-by: Damjan Marion <damarion@cisco.com>
diff --git a/src/vlib/init.h b/src/vlib/init.h
index e623565..364989e 100644
--- a/src/vlib/init.h
+++ b/src/vlib/init.h
@@ -171,6 +171,8 @@
 
 #define VLIB_INIT_FUNCTION(x) VLIB_DECLARE_INIT_FUNCTION(x,init)
 #define VLIB_WORKER_INIT_FUNCTION(x) VLIB_DECLARE_INIT_FUNCTION(x,worker_init)
+#define VLIB_NUM_WORKERS_CHANGE_FN(x)                                         \
+  VLIB_DECLARE_INIT_FUNCTION (x, num_workers_change)
 
 #define VLIB_MAIN_LOOP_ENTER_FUNCTION(x) \
   VLIB_DECLARE_INIT_FUNCTION(x,main_loop_enter)