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: NAndy Grover <andy.grover@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/rds/bind.c

@@ -187,6 +187,9 @@ int rds_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	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;
 	}