Added fixed entry for preventing IPv6 /116 pool migrations

Author: andystevensname

src/content/changelog/2019-10-07-api.md

@@ -42,4 +42,6 @@ Some heuristics for which heading to put API reference updates under:
 
 ### Fixed
 
-* Fixed a formatting error that prevented the [filtering and sorting](https://developers.linode.com/api/v4/#filtering-and-sorting) examples within the API documentation from correctly working as presented.
+* Fixed a formatting error that prevented the [filtering and sorting](https://developers.linode.com/api/v4/#filtering-and-sorting) examples within the API documentation from correctly working as presented.
+
+* Fixed an issue that allowed Linodes with IPv6 /116 pools to attempt to migrate to NGN data centers like Toronto and Mumbai. IPv6 /116 pools are not supported by NGN data centers, and so these migrations would never actually progress. A Linode with IPv6 /116 pools will now be prevented from initiating a migration to an NGN data center.