[pcap-ng-format] Can there be multiple "user application" option strings for an SHB?

[Hadriel Kaplan]

Need to decide if there can/can't be multiple shb_userappl options in
a given SHB.

If there can, then does the ordering matter - for example, if a
PCAP-NG file merger merges multiple SHBs into one, and adds the
merging machine's application info, does it prepend itself or append
itself to the list?

-hadriel