opcode IQUERY returns SERVFAIL instead of NOTIMP
Unsupported opcode must lead to
RCODE=NOTIMP. This will get back and bite us when the session signalling draft comes by.
Clarification: Response to unknown OPCODE must contain only the DNS message header and nothing else, not even EDNS. The reason is that different OPCODEs might potentially use very different message format so it is risky to return anything beyond the DNS header.
sets/resolver/iter_opcode_notimp.rpl in deckard, branch