neutron-vpnaas: Move permission to neutron-release/neutron-stable-maint
neutron-vpnaas: Move permission to neutron-release/neutron-stable-maint

After the recent governance change, tweak the ACL to be similar
to the other Neutron subprojects.

Change-Id: Id98260cbfa71e67c54a4c99d7c73cae6e344c687

openstack-infra/project-config,openstack-infra/project-config