tests: vpp_interface fix ip6 setter

Type: fix
Fixes: efd7bc2b1c8db160933ed3e9ab3cde0d07aaf863

Change-Id: I254f9fe44189f88621b9b0ff3f869efb9966ada5
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>
diff --git a/test/vpp_interface.py b/test/vpp_interface.py
index a671779..f92dc8e 100644
--- a/test/vpp_interface.py
+++ b/test/vpp_interface.py
@@ -89,7 +89,7 @@
 
     @local_ip6.setter
     def local_ip6(self, value):
-        self._local_ip6
+        self._local_ip6 = value
 
     @property
     def local_ip6_prefix_len(self):