message: Expose new cipher in factory
  Summary: QuicFizzFactory changes to expose the new header cipher.
diff: @@ -109,6 +109,8 @@ std::unique_ptr<PacketNumberCipher> QuicFizzFactory::makePacketNumberCipher(
  switch (cipher) {
  case fizz::CipherSuite::TLS_AES_128_GCM_SHA256:
  return std::make_unique<Aes128PacketNumberCipher>();
  + case fizz::CipherSuite::TLS_AES_256_GCM_SHA384:
  + return std::make_unique<Aes256PacketNumberCipher>();
  default:
  throw std::runtime_error("Packet number cipher not implemented");
  }
  