[NETLIKN]: Allow removing multicast groups.

Allow kicking listeners out of a multicast group when necessary
(for example if that group is going to be removed.)

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Patrick McHardy <kaber@trash.net>
Acked-by: Jamal Hadi Salim <hadi@cyberus.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index b971ddd..83d8239 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -162,6 +162,7 @@
 					  struct mutex *cb_mutex,
 					  struct module *module);
 extern int netlink_change_ngroups(struct sock *sk, unsigned int groups);
+extern void netlink_clear_multicast_users(struct sock *sk, unsigned int group);
 extern void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err);
 extern int netlink_has_listeners(struct sock *sk, unsigned int group);
 extern int netlink_unicast(struct sock *ssk, struct sk_buff *skb, __u32 pid, int nonblock);