RDS: Add a debug message suggesting to load transport modules

Now that RDS transports are no longer compiled-in to RDS core,
there is now the possibility that they will not be loaded. This
adds a helpful suggestion when rds_bind() fails to find a transport.

Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/rds/bind.c b/net/rds/bind.c
index c17cc39..5d95fc0 100644
--- a/net/rds/bind.c
+++ b/net/rds/bind.c
@@ -187,6 +187,9 @@
 	if (trans == NULL) {
 		ret = -EADDRNOTAVAIL;
 		rds_remove_bound(rs);
+		if (printk_ratelimit())
+			printk(KERN_INFO "RDS: rds_bind() could not find a transport, "
+				"load rds_tcp or rds_rdma?\n");
 		goto out;
 	}