rwrap: Make the rwrap_fake_* functions only fake RRs

rwrap: Make the rwrap_fake_* functions only fake RRs

The rwrap_fake_common() function did too much. Remove it and use
separate functions to add fake header and question sections. The
rwrap_fake_$RR functions will receive packet including the header and
question and only add its RR data.

This will allow recursive processing later.

Signed-off-by: Jakub Hrozek <jakub.hrozek@gmail.com>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Guenther Deschner <gd@samba.org>