relay: fix wrong invocation of router_readconfig

For some reason queuesize and batchsize were reversed, leading to wrong
numbers internally, but worse, breaking the any_of failover target
(issue #16), since the queue length maths no longer made sense.
relay: prevent batchsize being bigger than queuesize

Because the maths for any_of failover rely on batchsize being a fraction
of queuesize, make sure it cannot be configured to break.