gfe-relnote: n/a(code clean up) Add default definition of copy assignment for QuicPacketHeader.

This is to make QUICHE code compatible in GCC 9.2. Error was reported here: https://github.com/envoyproxy/envoy/issues/9437

PiperOrigin-RevId: 286631852
Change-Id: I15c645399078f0be81c2331d591d6f8975b9fc55
diff --git a/quic/core/quic_packets.h b/quic/core/quic_packets.h
index 9e97fa9..e8e1931 100644
--- a/quic/core/quic_packets.h
+++ b/quic/core/quic_packets.h
@@ -121,6 +121,8 @@
   QuicPacketHeader(const QuicPacketHeader& other);
   ~QuicPacketHeader();
 
+  QuicPacketHeader& operator=(const QuicPacketHeader& other);
+
   QUIC_EXPORT_PRIVATE friend std::ostream& operator<<(
       std::ostream& os,
       const QuicPacketHeader& header);