Nest: Forbid adding channels during reconfiguration
When a new channel is found during reconfiguration, do force restart of the protocol, like with any other un-reconfigurable change. The old behavior was that the new channel was added but remained in down state, even if the protocol was up, so a manual protocol restart was often necessary. In the future this should be improved such that a reconfigurable channel addition (e.g. direct) is accepted and channel is started, while an un-reconfigurable addition forces protocol restart.