dns: parse multiple txt segments into an array

dns: parse multiple txt segments into an array

A DNS TXT answer record can actually be made of up multiple TXT
entries in a single record. Suricata currently expands these into
multiple TXT records, however that is not very representative of the
actualy DNS message.

Instead, if a TXT record contains multiple labels, parse them into an
array.

We still expand multiple TXT segements into multiple TXT records at
logging time for compatibility, but this will allow something like
MDNS to log more accurately to the protocol.