QUIC: further limiting maximum QUIC packet size. quic-transport draft 29, section 14: QUIC depends upon a minimum IP packet size of at least 1280 bytes. This is the IPv6 minimum size [RFC8200] and is also supported by most modern IPv4 networks. Assuming the minimum IP header size, this results in a QUIC maximum packet size of 1232 bytes for IPv6 and 1252 bytes for IPv4. Since the packet size can change during connection lifetime, the ngx_quic_max_udp_payload() function is introduced that currently returns minimal allowed size, depending on address family.