Change [1] introduced support for advsvc role. This added
possibility for user with role advsvc to make CRUD operations
on ports, subnets and networks in foreign tenants.
Due the check in _validate_privileges() it was not working.
This patch fixes that.
Closes-Bug: #1796854
[1] https://review.openstack.org/#/c/101281
Change-Id: I6a3f91337bf8dd32012a75916e3409e30f46b50d