Doxy update

Here's some minor fixes related to doxygen. Only one that could worth to be discussed is https://github.com/regit/suricata/commit/e9dbf940e8c1418dda890f593778260f7b98e9d0

PR builds:
- PR build: https://buildbot.suricata-ids.org/builders/regit/builds/77
- PR pcaps: https://buildbot.suricata-ids.org/builders/regit-pcap/builds/15