Allow QuicSentPacketManager to expose the setter of num_ptos_for_path_degrading_.

This will allow Envoy to config the number of ptos it wants for path degrading alarm.

PiperOrigin-RevId: 405425564
diff --git a/quic/core/quic_sent_packet_manager.h b/quic/core/quic_sent_packet_manager.h
index b34aa20..ccd1e56 100644
--- a/quic/core/quic_sent_packet_manager.h
+++ b/quic/core/quic_sent_packet_manager.h
@@ -467,6 +467,10 @@
   QuicTime GetEarliestPacketSentTimeForPto(
       PacketNumberSpace* packet_number_space) const;
 
+  void set_num_ptos_for_path_degrading(int num_ptos_for_path_degrading) {
+    num_ptos_for_path_degrading_ = num_ptos_for_path_degrading;
+  }
+
  private:
   friend class test::QuicConnectionPeer;
   friend class test::QuicSentPacketManagerPeer;