rxrpc: Fix an overget of the conn bundle when setting up a client conn

When setting up a client connection, a second ref is accidentally obtained
on the connection bundle (we get one when allocating the conn and a second
one when adding the conn to the bundle).

Fix it to only use the ref obtained by rxrpc_alloc_client_connection() and
not to add a second when adding the candidate conn to the bundle.

Fixes: 245500d8 ("rxrpc: Rewrite the client connection manager")
Signed-off-by: David Howells <dhowells@redhat.com>