This resolves a number of issues that were keeping communications with
foreign ships from working.
- there was no link-update mark
- there was no +on-arvo handling in link-listen-hook
- link-listen-hook was subscribing to the non-existent "link-hook"
- link-proxy-hook permission check was looking at a wrong path
Also makes link-listen-hook aware that subscriptions might get rejected
because of permissions, so that it ignores failed subscriptions instead
of being loud about it.
