Reentrancy: adns__internal_submit does list handling

Move the formulaic queue management from the call sites to
adns__internal_submit.  The requirement to do this wasn't mentioned in
adns__internal_submit's comment, and now that it's not there it
probably isn't worth remarking on.

No ultimate functional change.

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