Fix binary compatibility of string conversion of RRs with internl addr tables

Fix binary compatibility of string conversion of RRs with internl addr tables

Queries without adns__qtf_bigaddr use a smaller stride than the
size of our own adns_rr_addr.  This is dealt with by explicit
calculation of the addr struct using the stride from gsz_addr.

However, this circumlocution was omitted in cs_hostaddr, with the
result that adns_rr_info would go wrong for old clients.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>