Fix the hacking errors present since neutron-lib 3.21.1

This new neutron-lib 3.21.1 version includes several new hacking checks.
Because the eventlet removal is not finished, the N535 is skipped.

Signed-off-by: Rodolfo Alonso Hernandez <ralonsoh@redhat.com>
Change-Id: Iaad3e87874838eb75d2f6789e71030eda8c587a0
diff --git a/tox.ini b/tox.ini
index 21574f4..e209d58 100644
--- a/tox.ini
+++ b/tox.ini
@@ -62,8 +62,9 @@
 # E129 visually indented line with same indent as next logical line
 # I202 Additional newline in a group of imports.
 # N530 direct neutron imports not allowed
+# N535 prevent eventlet library import
 # W504 line break after binary operator
-ignore = E126,E128,E129,I202,N530,W504
+ignore = E126,E128,E129,I202,N530,N535,W504
 # H106: Don't put vim configuration in source files
 # H203: Use assertIs(Not)None to check for None
 # H204: Use assert(Not)Equal to check for equality