reverse parsing: Pass dgram and labstart instead of label

[adns] / regress / case-longlab1.out

adns debug: using nameserver 172.18.45.6
hyrndrobwlxxxxxxxxxxlllantysiliogogllanfairpwllgwyngyllgogerychw.relativity.greenend.org.uk. flags 1 type 1 A(-) submitted
hyrndrobwlxxxxxxxxxxlllantysiliogogllanfairpwllgwyngyllgogerychw.relativity.greenend.org.uk. flags 1 type A(-): Domain name or component is too long; nrrs=0; cname=$; owner=$; ttl=604800
rc=0