l2tp : multicast notification to the registered listeners

From: Bill Hong <[email protected]>

Previously l2tp module did not provide any means for the user space to get notified when tunnels/sessions are added/modified/deleted. This change contains the following
- create a multicast group for the listeners to register.
- notify the registered listeners when the tunnels/sessions are created/modified/deleted.

@@ -178,5 +178,6 @@ enum l2tp_seqmode {
  */
 #define L2TP_GENL_NAME		"l2tp"
 #define L2TP_GENL_VERSION	0x1
+#define L2TP_GENL_MCGROUP       "l2tp"
 
 #endif /* _UAPI_LINUX_L2TP_H_ */

From: Stephen Hemminger <[email protected]>
Date: Sat, 27 Dec 2014 10:12:39 -0800

Applied.