No more sending "all-channel" errors; in particular, gossipd now only
sends warnings (which make us hang up), not errors, and peer_connected
rejections are warnings (and disconnect), not errors.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Changed: Plugins: `peer_connected` rejections now send a warning, not an error, to the peer.