bugsquash: Fixed wrong compression offset.

- It makes no sense to move compression offset for RDLENGTH bytes for each type, the value was totally wrong.
- It would work fine for single RRs, but if there were more than one, and if a comprimable DNAME appeared for the first time in the packet, later references to this DNAME would be broken.

Change-Id: Ic02351625d5a4e120b492946759607583502967f