/// <param name="discoveredDevice">A <see cref="DiscoveredSsdpDevice"/> instance representing the device that has become unavailable.</param>
/// <param name="expired">A boolean value indicating whether this device is unavailable because it expired, or because it explicitly sent a byebye notification.. See <see cref="Expired"/> for more detail.</param>
/// Returns true if the device is considered unavailable because it's cached information expired before a new alive notification or search result was received. Returns false if the device is unavailable because it sent an explicit notification of it's unavailability.