cmd/tsp-forwarder: prevent overconsumption of CPU

[masiulaniec]

GOMAXPROCS default is changing, see the proposal at https://golang.org/s/go15gomaxprocs

In response to this, I think cmd/tsp-forwarder should call runtime.GOMAXPROCS(1). It should be enough for everybody, because the heavy-lifting is done by cmd/tsp-poller and cmd/tsp-aggregator.

This is partially a security feature, because CPU consumption is affected by tsp-controller (think Filter rules), and therefore can be potentially compromised and used as a DoS attack vector.