push channel monitor doesn't stop transfer completes

[dirkmc]

When the data transfer completes, or the deal fails during a data transfer, for example if the provider rejects the transfer, the client's push channel monitor doesn't always stop.

Observed when the provider had an error accepting the deal and the client received "response rejected"

list-transfers shows that the data transfer is in the Failed state, but the channel monitor is still running.

Also observed when a deal completed, the push channel monitor was still logging that it's checking the data rate. It should stop checking the data rate when the transfer completes.

[dirkmc]

Fixed by #171