s3: libsmb: Add in (currently unused) function dns_lookup_list().

This function takes a list of names returned from a DNS SRV
query which didn't have returned IP addresses and returns an
array of struct sockaddr_storage.

Currently synchronous, but this is the function that will
be changed to be asynchronous later.

Compiles but commented out for now so we don't get "unused
function" warnings.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Isaac Boukris <iboukris@samba.org>
