pcap multi v4.3

Implements 'multi' mode in 'pcap-log', so that each thread records to it's own pcap file.

Prscript:
- PR build: https://buildbot.suricata-ids.org/builders/inliniac/builds/325
- PR pcaps: https://buildbot.suricata-ids.org/builders/inliniac-pcap/builds/240