Under this spec, an error with an all-zero channel id is ignored.
Warnings, being odd, will be ignored by older nodes too.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

…e connection.

And make most places warn or error.  Places where we're operating
on a channel tend to be "warn and close connection" since we want to
forget the mistake they just sent, and closing the connection does that.

We now use the same words everywhere:
1. "fail channel" means to go onchain (if necessary).
2. "send `error`" means to send an error message.
3. "send `warning`" means to send a warning message.
4. "close connection" means close the connection.

These are all spelled out explicitly, rather than having "fail channel"
imply sending an error packet, for example.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Co-authored-by: Bastien Teinturier <31281497+t-bast@users.noreply.github.com>

Abandoning channel is kinda what they want here.

Reported-by: Matt Corallo
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

There were valid uses for "I don't want to talk to you anymore" apparently!

Also fixed some tabs -> spaces.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>