rds: Use RCU for the bind lookup searches

The RDS bind lookups are somewhat expensive in terms of CPU
time and locking overhead.  This commit changes them into a
faster RCU based hash tree instead of the rbtrees they were using
before.

On large NUMA systems it is a significant improvement.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/net/rds/rds.h b/net/rds/rds.h
index c22bd7b..241a085 100644
--- a/net/rds/rds.h
+++ b/net/rds/rds.h
@@ -452,7 +452,7 @@
 	 * bound_addr used for both incoming and outgoing, no INADDR_ANY
 	 * support.
 	 */
-	struct rb_node		rs_bound_node;
+	struct hlist_node	rs_bound_node;
 	__be32			rs_bound_addr;
 	__be32			rs_conn_addr;
 	__be16			rs_bound_port;