Lease query uses the link address only to identify a link

There was a confusion between the link address in lease query amplified by the by-link-address new query type of bulk lease query and the link address field of relay messages.

So instead of using the relay message field as a key for new BLQ methods we should convert the link address of the lease query into a prefix and length which narrow addresses of leases to retrieve, simplifying a bit the current code.