c-lightning should not disconnect when receiving a warning during quick close

[t-bast]

This is related to lightning/bolts#904
Since c-lightning already supports warning messages, we should do this right now.

When c-lightning receives a warning during quick close (usually because the peer doesn't agree with the fee_range c-lightning sent), we really should not disconnect. If we stay connected and the node operator reads the warning message, they can reuse the close API to change the fee_range to something that the peer will agree with, and the mutual close is able to make progress.

But right now since c-lightning disconnects, on reconnection it will re-send the same fee_range automatically so it will instantly disconnect again, not giving the node operator an opportunity to update the fee_range.

[rustyrussell]

Yes, we should update if they try to close again... but not disconnecting would be weird? We have nothing useful to say at this point.

[rustyrussell]

(We always close after a warning, for this reason)

[t-bast]

In that case you should allow the node operator to call the close API while disconnected, that would work as well indeed.

[sangbida]

This issue is being closed as part of issue cleanup.

Reason: Mentioned in git commits (likely fixed); About deprecated feature

If you believe this issue should remain open, please comment and we can reopen it.