Merge "return cached value for call id instead of calling AIDL" into udc-dev

     * Gets the call ID of the session.

     *

     * @return the call ID

     * If null is returned for getCallId, then that means that the call ID has not been set yet.

     */

    public String getCallId() {

        if (mClosed) {

        sb.append("[ImsCallSession objId:");

        sb.append(System.identityHashCode(this));

        sb.append(" callId:");

        sb.append(getCallId());

        sb.append(mCallId != null ? mCallId : "[UNINITIALIZED]");

        sb.append("]");

        return sb.toString();

    }