bridge: add netlink notification on forward entry changes

This allows applications to query and monitor bridge forwarding
table in the same method used for neighbor table. The forward table
entries are returned in same structure format as used by the ioctl.
If more information is desired in future, the netlink method is
extensible.

Example (using bridge extensions to iproute2)
  # br monitor

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index a0e6b94..884d245 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -354,6 +354,7 @@
 extern void br_fdb_update(struct net_bridge *br,
 			  struct net_bridge_port *source,
 			  const unsigned char *addr);
+extern int br_fdb_dump(struct sk_buff *skb, struct netlink_callback *cb);
 
 /* br_forward.c */
 extern void br_deliver(const struct net_bridge_port *to,