QUIC: removed "quic_mtu" directive. The directive used to set the value of the "max_udp_payload_size" transport parameter. According to RFC 9000, Section 18.2, the value specifies the size of buffer for reading incoming datagrams: This limit does act as an additional constraint on datagram size in the same way as the path MTU, but it is a property of the endpoint and not the path; see Section 14. It is expected that this is the space an endpoint dedicates to holding incoming packets. Current QUIC implementation uses the maximum possible buffer size (65527) for reading datagrams.