remove runmode auto v2

Remove 'auto' runmodes.
Set workers as the default for af-packet.
Af-packet 'threads' defaults to 'auto', which sets up threads for the number of cores.

Prscript:
- PR build: https://buildbot.openinfosecfoundation.org/builders/inliniac/builds/68
- PR pcaps: https://buildbot.openinfosecfoundation.org/builders/inliniac-pcap/builds/68

cc: @regit