@Override
    public String generateNetworkId(@NonNull final byte[] networkKey) {
        return MeshParserUtils.bytesToHex(SecureUtils.calculateK3(networkKey), false);
    }
Appends the PDUs that are segmented at gatt layer.

@param mtuSize mtu size supported by the device/node
@param pdu     pdu received by the provisioner
@return the combine pdu or returns null if not complete.
mesh/src/main/java/no/nordicsemi/android/mesh/MeshManagerApi.java