Add test cases for 933d429

Previously we didn't test this particular case and we found a bug in our
validation. Now let's add an example of it as a valid host name so we do
actually test and prove that it is valid.

Author: sigmavirus24

tests/conftest.py

@@ -15,6 +15,7 @@
     '[21DA:D3:0:2F3B:2AA:FF:FE28:9C5A]',
     '[FE80::2AA:FF:FE9A:4CA2]',
     '[FF02::2]',
+    '[FFFF::]',
     '[FF02:3::5]',
     '[FF02:0:0:0:0:0:0:2]',
     '[FF02:30:0:0:0:0:0:5]',