why logical_router lb not supoort logical_router options snat-ct-zone

[yangzhaowu1]

if lb attach to logical_router, he ingress action in sb flows is ct_lb, the engress action in sb flows is ct_dnat_in_zone. ct_lb always is MFF_LOG_DNAT_ZONE, if snat-ct-zone is not set, ct_dnat_in_zone=MFF_LOG_DNAT_ZONE; if snat-ct-zone is set, ct_dnat_in_zone=MFF_LOG_SNAT_ZONE.
so if logical router is set options:snat-ct-zone=xx. ingress ct_zone is MFF_LOG_DNAT_ZONE；engress ct_zone is MFF_LOG_SNAT_ZONE；ingress ct_zone not match engress ct_zone cause lr_lb not support snat-ct-zone