restrict the cases of STYPE == RRSIG
- Jumping xNAMEs makes no sense, because that would only give us signatures for other names than requested. - Spawning RRSIG sub-query of an RRSIG (sub-)query seems not good.
- Jumping xNAMEs makes no sense, because that would only give us signatures for other names than requested. - Spawning RRSIG sub-query of an RRSIG (sub-)query seems not good.