A new flag is added so that we can either expose all the
tenant network IPs (expose_tenant_networks) or just the
IPv6 GUA ones (expose_ipv6_gua_tenant_networks).
If the expose_ipv6_gua_tenant_network flag is enabled, before
exposing the tenant IPs it is checked if they are IPv6 and
of global type, and only in that case they will be advertized.
Story 2010374
Task 46609
Change-Id: Ifa1e25aabb3f6a3fc5f1e5ba5a32bfedadf6765a
d6686c88e6