Make DNS report failure on all packet construction errors

Make DNS report failure on all packet construction errors

The attached patch alters the DNS lookup behaviour to abort with an error
in ALL cases where the rfc1035 library generates an error (negative result).

I'm not sure there is any noticable effect other than better code. The
error case *should* in old code be picked up on the initial packet
construction rather than the repeat packet. This may have been incorrect
given that the packet type is changing between A/AAAA.