Stop sending ICMP unreachable messages when rejecting TCP connections.

These messages cause log spam on rejected stubby client connections
because stubby clients consider this an uncommon message and log each
time they receive one.

Protected by FLAGS_qbone_send_icmp_on_tcp_rst.

PiperOrigin-RevId: 381306450
diff --git a/quic/qbone/qbone_packet_processor.cc b/quic/qbone/qbone_packet_processor.cc
index 7b45ed1..6e83e76 100644
--- a/quic/qbone/qbone_packet_processor.cc
+++ b/quic/qbone/qbone_packet_processor.cc
@@ -103,6 +103,10 @@
       SendTcpReset(*packet, direction);
       stats_->OnPacketDroppedWithTcpReset(direction);
       break;
+    case ProcessingResult::TCP_RESET:
+      SendTcpReset(*packet, direction);
+      stats_->OnPacketDroppedWithTcpReset(direction);
+      break;
   }
 }
 
diff --git a/quic/qbone/qbone_packet_processor.h b/quic/qbone/qbone_packet_processor.h
index c85280f..8c2375a 100644
--- a/quic/qbone/qbone_packet_processor.h
+++ b/quic/qbone/qbone_packet_processor.h
@@ -46,6 +46,8 @@
     // RST requires information from the current connection state to be
     // well-formed.
     ICMP_AND_TCP_RESET = 4,
+    // Send a TCP RST.
+    TCP_RESET = 5,
   };
 
   class OutputInterface {