DNS_PACKET_PAYLOAD_SIZE_MAX is limiting the size of the stub replies to
512 with EDNS off or 4096 with EDNS on, without checking the protocol
used. This makes TCP replies for clients without EDNS support to be
limited to 512, making the truncate flag useless if the query result is
bigger than 512 bytes.
This commit increases the size of TCP replies to DNS_PACKET_SIZE_MAX