add unknown nsi error class, as we just sometimes get a bad error code and opennsa should explode over that
add unknown nsi error class, as we just sometimes get a bad error code and opennsa should explode over that

jab1982/opennsa,NORDUnet/opennsa,NORDUnet/opennsa,jab1982/opennsa,NORDUnet/opennsa