release notes update for db schema change

[aquerubin]

Reminder that the post-2.9 release notes will need to mention several database fields have changed to accomodate IPv6 addresses and an existing database will need to be updated.

IP addresses are now stored in the database as character strings instead of integers. To convert an existing database, run the convert-db-ipv6.sql script (found in src/os_dbd).