Add unknown state in DataSubscriptionState enum

/**

 * Used for pull network statistics via mobile|wifi networks, and sliced by interesting dimensions.

 * Note that data is expected to be sliced into more dimensions in future. In other words,

 * the caller must not assume the data is unique when filtering with a set of matching conditions.

 * Thus, as the dimension grows, the caller will not be affected.

 * Note that the data is expected to be sliced into more dimensions in future. In other words,

 * the caller must not assume any row of data is one full report when filtering with a set of

 * matching conditions, because future data may represent with multiple rows what is currently

 * represented by one.

 * To avoid being broken by future slicing, callers must take care to aggregate rows even if they

 * query all the existing columns.

 *

 * Pulled from:

 *   StatsPullAtomService (using NetworkStatsService to get NetworkStats)

    optional int32 rat_type = 6;

    // Mcc/Mnc read from sim if the record is for a specific subscription, null indicates the

    // record is combined regardless of subscription.

    // record is combined across subscriptions.

    optional string sim_mcc = 7;

    optional string sim_mnc = 8;

    // Allows mobile virtual network operators (MVNOs) to be identified with individual IDs.

    // See TelephonyManager#getSimCarrierId.

    optional int32 carrier_id = 9;

    // Enumeration of opportunistic states with an additional ALL state indicates the record is

    // combined regardless of the boolean value in its field.

    enum DataSubscriptionState {

        UNKNOWN = 0; // For server side backward compatibility.

        ALL = 1;

        OPPORTUNISTIC = 2;

        NOT_OPPORTUNISTIC = 3;

    }

    // Mark whether the subscription is an opportunistic data subscription, and ALL indicates the

    // record is combined regardless of opportunistic data subscription.

    // record is combined across opportunistic data subscriptions.

    // See {@link SubscriptionManager#setOpportunistic}.

    optional DataSubscriptionState opportunistic_data_sub = 9;

    optional DataSubscriptionState opportunistic_data_sub = 10;

}

/**