@Override
    public int getOpCode() {
        return OP_CODE;
    }
Constructs ConfigHeartbeatSubscriptionSet message.

@param srcAddress Source address identifies the Heartbeat Subscription Source,
                  where the address shall be an unassigned address or a unicast address.
                  All other values are prohibited.
@param dstAddress Destination address identifies the Heartbeat Subscription destination,
                  where the address shall be an unassigned address,
                  the primary unicast address of the node, or a group address,
                  all other values are Prohibited.
@param periodLog  Period for sending Heartbeat messages.
@throws IllegalArgumentException if any illegal arguments are passed.
mesh/src/main/java/no/nordicsemi/android/mesh/transport/ConfigHeartbeatSubscriptionSet.java