Lease Query by address for delegated prefixes
Implement the last part of this (quoting RFC 5007):
Query by IPv6 address - This query allows a requestor to request
from a server the bindings for a client that either is bound to
the address or has been delegated the prefix that contains the
address.
The problem is that Kea does not track PD leases so there is nothing immediately usable to support this.
Some ideas:
- use a patricia tree: this will give the answer in O(1) but the tree has to be filled at startup or first use and maintained
- determine what pd pool the prefix is from. A bit easier with a link address as it will limit the number of subnets so the number of pd pools. The fact the pd pool can be large is not really a problem because the candidate start address of the prefix can be computed. Of course this does not work for reservations.
The goal is to perform at most one getLease6 which is the expensive part.
Can be related to #1958 (closed) in particular for pool base solutions. For patricia tree see #2256