Allow long connection IDs for unknown QUIC versions

In particular, if we're a server and a client sends us a packet with an unknown version and a connection ID of any length between 8 and 255, we must respond with a version negotiation packet that includes that same connection ID.

gfe-relnote: allow longer connection IDs, protected by new disabled flag gfe2_restart_flag_quic_allow_very_long_connection_ids
PiperOrigin-RevId: 286015388
Change-Id: I53ff4e602a19f30f56aba10ad7d877776597a5cf

quic/core/quic_data_writer_test.cc

diff --git a/quic/core/quic_data_writer_test.cc b/quic/core/quic_data_writer_test.cc
index 7cfde88..3c38673 100644
--- a/quic/core/quic_data_writer_test.cc
+++ b/quic/core/quic_data_writer_test.cc
@@ -1166,6 +1166,9 @@
 }
 
 TEST_P(QuicDataWriterTest, InvalidConnectionIdLengthRead) {
+  SetQuicRestartFlag(quic_allow_very_long_connection_ids, false);
+  // TODO(dschinazi) delete this test when we deprecate
+  // quic_allow_very_long_connection_ids.
   static const uint8_t bad_connection_id_length = 200;
   static_assert(
       bad_connection_id_length > kQuicMaxConnectionIdAllVersionsLength,