docs: typo in netns docs
docs: typo in netns docs

Bug-Url: https://github.com/svinota/pyroute2/issues/179

tomislacker/python-iproute2,tomislacker/python-iproute2,drzaeus77/pyroute2,roolebo/pyroute2,roolebo/pyroute2,mtiny/pyroute2,mtiny/pyroute2,drzaeus77/pyroute2