tipc: introduce link entry structure to struct tipc_node

struct 'tipc_node' currently contains two arrays for link attributes,
one for the link pointers, and one for the usable link MTUs.

We now group those into a new struct 'tipc_link_entry', and intoduce
one single array consisting of such enties. Apart from being a cosmetic
improvement, this is a starting point for the strict master-slave
relation between node and link that we will introduce in the following
commits.

Reviewed-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/tipc/bcast.c b/net/tipc/bcast.c
index a816382..59b2f2a 100644
--- a/net/tipc/bcast.c
+++ b/net/tipc/bcast.c
@@ -413,7 +413,7 @@
 	 * all nodes in the cluster don't ACK at the same time
 	 */
 	if (((seqno - tn->own_addr) % TIPC_MIN_LINK_WIN) == 0) {
-		tipc_link_proto_xmit(node->active_links[node->addr & 1],
+		tipc_link_proto_xmit(node_active_link(node, node->addr),
 				     STATE_MSG, 0, 0, 0, 0);
 		tn->bcl->stats.sent_acks++;
 	}