Implement MAC Flush for BD or Interface from the L2FIB

Allow non-static MACs in the L2FIB which is associated with an
interface or a bridge domain (BD) be flushed. MAC flush are
initiated automatically when an interface is removed from a BD
or when a BD is deleted. MAC flush can also be invoked manually
via the following CLI:
 l2fib mac-flush interface <if-name>
 l2fib mac-flush bridge-domain <bd-id>

Change-Id: Ie33243622834810a765f48ebcd22bdb8e8fc87a4
Signed-off-by: John Lo <loj@cisco.com>
diff --git a/src/vnet/l2/l2_learn.h b/src/vnet/l2/l2_learn.h
index 5bb1130..0d95de0 100644
--- a/src/vnet/l2/l2_learn.h
+++ b/src/vnet/l2/l2_learn.h
@@ -51,6 +51,7 @@
 {
   L2_MAC_AGE_PROCESS_EVENT_START = 1,
   L2_MAC_AGE_PROCESS_EVENT_STOP = 2,
+  L2_MAC_AGE_PROCESS_EVENT_ONE_PASS = 3,
 } l2_mac_age_process_event_t;
 
 #endif