MapGrant
data class MapGrant(val tcp: Boolean, val internalPort: Int, val externalPort: Int, val lifetimeSeconds: Long)
The outcome of a successful mapDetailed: the public port the gateway granted and the lease lifetime it actually assigned (which may differ from what was requested: on_reply adopts both public_port and lifetime from the response). The engine schedules its lease-refresh timer from lifetimeSeconds.