CLOUDSTACK-6079 suppress updates of public traffic type's broadcast type if traffic type is not public

fixed issue: if public traffic is on a physical network isolated by VLAN,
and guest traffic is on an another physical network isolated by VXLAN,
public traffic's broadcast type is updated to VXLAN by mistake.
CLOUDSTACK-6072 bugfix: vxlan networks not deallocating vnet ids

made GuestNetworkGuru release VNI during network shutdown.