tipc: make subscriber server support net namespace

TIPC establishes one subscriber server which allows users to subscribe
their interesting name service status. After tipc supports namespace,
one dedicated tipc stack instance is created for each namespace, and
each instance can be deemed as one independent TIPC node. As a result,
subscriber server must be built for each namespace.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Tested-by: Tero Aho <Tero.Aho@coriant.com>
Reviewed-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/core.h

@@ -106,6 +106,10 @@ struct tipc_net {
 	/* Name table */
 	spinlock_t nametbl_lock;
 	struct name_table *nametbl;
+
+	/* Topology subscription server */
+	struct tipc_server *topsrv;
+	atomic_t subscription_count;
 };
 
 #ifdef CONFIG_SYSCTL