Return the counterparty node_id as a part of a force-shutdown res

Return the counterparty node_id as a part of a force-shutdown res

In the coming commits we'll need the counterparty node_id when
handling a background monitor update as we may need to resume
normal channel operation as a result. Thus, we go ahead and pipe it
through from the shutdown end, as it makes the codepaths
consistent.

Sadly, the monitor-originated shutdown case doesn't allow for a
required counterparty node_id as some versions of LDK didn't have
it present in the ChannelMonitor.