Use valid DNS queries as largest UDP and TCP test payloads

EDNS0 option PADDING is used to inflate the queries.
Largest UDP payload over IPv4 is 65507 bytes, 65527 for the IPv6.
We go with IPv4. Oversized payloads are already tested using largest TCP
payload (65535 bytes).

Generated with dnspython 2.6.1:
    import dns.message
    m = dns.message.make_query('.', 'TYPE666')
    print(len(m.to_wire(max_size=65535)))
    m.options.append(dns.edns.GenericOption(dns.edns.OptionType.PADDING, '\x00' * 65475))
    print(len(m.to_wire(max_size=65535)))
    binary = m.to_wire(max_size=65535)

    import struct
    binary = struct.pack('>H', len(binary)) + binary
    open('output.blob', 'wb').write(binary)