As per [1], neutron-lib 0.3.0 provides a public add/get API for
local validator registration/access. This API is preferred over
directly accessing the validators dict module-level attribute
that's done today when adding a new validator and in fact
direct access to the validators dict is deprecated.
This patch changes all vmware-nsx's usage of the validators dict
to use the public API.
Related-Bug: #1584237
[1] https://review.openstack.org/#/c/324090/
Change-Id: Ifc403d41133eefb1dfbcd31952c7a88c436e9724
bf72494d00