Runmodes: remove 'auto' runmodes

Remove 'auto' runmodes from all capture methods. It wasn't reliable
enough, as it didn't enforce inspection order of packets.
threading: remove '1slot' functions

No longer in use after the 'auto' runmode removal.

All runmodes now use either varslot or pktacqloop support.
Runmode: handle value 'auto'

Auto now selects the default runmode for the capture method.
af-packet: threads: auto, default to workers

Add a new default value for the 'threads:' setting in af-packet: "auto".
This will create as many capture threads as there are cores.

Default runmode of af-packet to workers.
util-ioctl: Add function to get number of RSS queues on iface

The number of RSS queues can be fetched via a standard ioctl which
is independant of hardware.
util-ioctl: add message in case of failure
af-packet: no more threads than RSS queues

If we manage to read the number of RSS queues from an interface,
this means that the optimal number of capture threads is equal
to the minimum of this number and of the number of cores on the
system.

This patch implements this logic thanks to the newly introduced
function GetIfaceRSSQueuesNum.