dissect the alphanumeric message that's part of operation 30
Bug: 10464

Change-Id: I1a42877ee549b40e0c739dd2d1cbe4615ed9b9bd
Reviewed-on: https://code.wireshark.org/review/4098
Reviewed-by: Martin Kaiser <wireshark@kaiser.cx>
Tested-by: Martin Kaiser <wireshark@kaiser.cx>