resolver: construct comm_addr; honour multiple addresses from the resolver

resolver: construct comm_addr; honour multiple addresses from the resolver

We move construction of the comm_addr into the resolver.  The comm_if
and port are supplied to it by site and filled in by the resolver.
This allows the resolver to return a complete comm_addr array.

While we're here, we make an adns_r_addr query instead of an adns_r_a
query.

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