[pyroute2.NetNS] Not honoring flags since pyroute2>0.8.1

[karelyatin]

In OpenStack neutron we have a periodic job running with pyroute2 master(currently at commit e106ce4) and since the merge of thread-unsafe branch in master the job started to fail https://bugs.launchpad.net/neutron/+bug/2092722 as the tests expects the namespace to not be created when flags=0 is passed.

The failure is related to NetNS not honoring flags(like 0 to not create netns)

Reproducer:-
import pyroute2
from pyroute2 import netns
try:
pyroute2.NetNS('netns-test', flags=0)
print("Namespace created")
except FileNotFoundError:
print("Namespace do not exist, creating...")
pyroute2.NetNS('netns-test', flags=64)
print("Removing namespace")
netns.remove('netns-test')

With master branch it do not honor flags=0 and creates the network namespace.
Namespace created
Removing namespace

With 0.8.1 it do not create network namespace if flags=0 is passed
Namespace do not exist, creating...
Removing namespace