DNS seeds have been down/offline for a while, and this code (which
blocks!) has been a source of trouble. We should probably use a
canned set of "known nodes" if we want to bootstrap.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Changed: Protocol: we no longer use DNS seeds for peer lookup fallbacks.
Fixes: https://github.com/ElementsProject/lightning/issues/7913