[master] Added ChangeLog entry for #5009.

ChangeLog

+1175.	[bug]		marcin
+	Corrected a bug whereby a client, for which there was no
+	host reservation specified, did not obtain an IPv6 lease
+	from a server when PostgreSQL or MySQL host database backend
+	was in use. In addition, PostgreSQL host database backend
+	allows for specifying NULL values in certain columns within
+	host reservation tables.
+	(Trac #5009, git d3109bb27786867fdc99954ba55367f0ad129e7a)
+
 1174.	[bug]		tmark
 	Modifed kea-dhcp6 to avoid requesting DNS updates when
 	existing leases are renewed without changes to the FQDN.