Add multiqueue status to the QBONE bonnet server status page.

The /statusz page will show the number of active queues (primary plus data-only), the eBPF steering state (attached, detached, or fallback to single-queue), and the health of each queue.

PiperOrigin-RevId: 992389157

quiche/quic/qbone/bonnet/qbone_tunnel_interface.h

diff --git a/quiche/quic/qbone/bonnet/qbone_tunnel_interface.h b/quiche/quic/qbone/bonnet/qbone_tunnel_interface.h
index 07ffaa0..6896467 100644
--- a/quiche/quic/qbone/bonnet/qbone_tunnel_interface.h
+++ b/quiche/quic/qbone/bonnet/qbone_tunnel_interface.h
@@ -94,6 +94,8 @@
   virtual std::string HealthString() = 0;
 
   virtual std::string ServerRegionString() = 0;
+
+  virtual std::string MultiqueueStatusString() const { return ""; }
 };
 
 }  // namespace quic