RDS: Track transports via an array, not a list

Now that transports can be loaded in arbitrary order,
it is important for rds_trans_get_preferred() to look
for them in a particular order, instead of walking the list
until it finds a transport that works for a given address.
Now, each transport registers for a specific transport slot,
and these are ordered so that preferred transports come first,
and then if they are not loaded, other transports are queried.

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

net/rds/tcp.c

@@ -271,6 +271,7 @@ struct rds_transport rds_tcp_transport = {
 	.exit			= rds_tcp_exit,
 	.t_owner		= THIS_MODULE,
 	.t_name			= "tcp",
+	.t_type			= RDS_TRANS_TCP,
 	.t_prefer_loopback	= 1,
 };