gfe-relnote: In IETF QUIC draft 25+, default to 1 packet per PTO, skip a packet number and 1st PTO to be std::max(1.5 * srtt, srtt + 4 * rttvar + ack_delay). Protected by existing gfe2_reloadable_flag_quic_enable_version_draft_25_v3. PiperOrigin-RevId: 300377945 Change-Id: I029b1709a852542124d8068bc4f7003f674c625a