[master] Added ChangeLog entry for #5307.

ChangeLog

+1302.	[func]		marcin, tomek
+	DHCPv6 server supports shared networks. It allows for grouping
+	multiple subnets and use them interchangeably to allocate
+	IP addresses and other resources to a client located on the
+	particular link. This mechanism is useful to extend an
+	address space for the client belonging to a particular
+	subnet and/or to segregate clients being on the same link but
+	belonging to different classes, e.g. cable modem vs router.
+	(Trac #5307, git 110d0c9e403af28e6810141f978d9bf55c381f14)
+
 1301.	[func]		fdupont
 	Added some standard option definitions which are supported
 	by ISC DHCP but not (yet) by Kea.