Passive peers: configured, and left to connect

A session could only be configured for a peer we would then dial, every
few seconds to two minutes, for as long as it was not up. A new peer
whose side was not ready yet filled the log with failed attempts, and a
peer that opens its sessions itself was dialled for nothing.

A peer with `passive: true` is not dialled. A connection from its address
is taken as for any configured peer, and the session comes up with all
that is configured for it: role, import policy, export limits,
hold-downs. Until then the status page and /api/peers show it as
`Passive`, waiting for the peer to connect; after a session, with how
that session ended, which nothing else would say since nobody dials it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/web/static/statusz.html

@@ -242,7 +242,7 @@ from <select id="lookup-peer"><option value="">any peer</option></select>
     tick();
   }
 
-  const STATE_CLASS = { Established: 'ok', Connecting: 'warn', Backoff: 'bad', Idle: 'dim' };
+  const STATE_CLASS = { Established: 'ok', Connecting: 'warn', Backoff: 'bad', Idle: 'dim', Passive: 'dim' };
   // Where several routes for a prefix are exchanged (ADD-PATH), and which way.
   function addPath(p) {
     const rx = p.add_path_receive || [], tx = p.add_path_send || [];
@@ -260,7 +260,9 @@ from <select id="lookup-peer"><option value="">any peer</option></select>
       const up = p.state === 'Established';
       const restarting = !up && p.stale_until_unix
         ? `<span class="warn" title="Graceful restart: the peer's routes are kept, and used, until it is back and has sent them again">restarting: ${p.stale_routes} routes kept for ${until(p.stale_until_unix)}</span>` : '';
-      const detail = [restarting, p.state === 'Backoff' ? `${esc(p.last_error || '')}; retry in ${until(p.retry_at_unix)}` : '']
+      const detail = [restarting,
+        p.state === 'Backoff' ? `${esc(p.last_error || '')}; retry in ${until(p.retry_at_unix)}` : '',
+        p.state === 'Passive' ? `waiting for the peer to connect${p.last_error ? `; last session: ${esc(p.last_error)}` : ''}` : '']
         .filter(Boolean).join('; ');
       const gr = p.graceful_restart;
       const graceful = gr ? ` &middot; <span title="Graceful restart (RFC 4724): the peer says a restart takes ${gr.restart_time_secs}s${gr.notification ? ', and NOTIFICATIONs other than Hard Reset count as restarts (RFC 8538)' : ''}">graceful restart</span>` : '';