Relax permissions for API prefix usage endpoint

Needed for subnet matrix tool to work for non-admin users

This bug was introduced in c2b9002

Author: johannaengland

changelog.d/3374.fixed.md

@@ -0,0 +1 @@
+Relax permissions for API prefix usage view endpoint

python/nav/web/api/v1/views.py

@@ -921,6 +921,9 @@ class PrefixUsageList(NAVAPIMixin, ListAPIView):
     # RelatedOrderingFilter does not work with the custom pagination
     filter_backends = (filters.SearchFilter, DjangoFilterBackend)
 
+    # Logged-in users must be able to access this API to use the subnet matrix tool
+    permission_classes = (RelaxedPermission,)
+
     def get(self, request, *args, **kwargs):
         """Override get method to verify url parameters"""
         get_times(request)