Add more suricata.yaml configuration options for mPIPE.

Add two new mPIPE load-balancing configuration options in suricata.yaml.
1) "sticky" which keep sending flows to one CPU, but if that queue is full,
don't drop the packet, move the flow to the least loaded queue.
2) Round-robin, which always picks the least full input queue for each
packet.

Allow configuring the number of packets in the input queue (iqueue) in
suricata.yaml.

For the mPipe.buckets configuration, which must be a power of 2, round
up to the next power of two, rather than report an error.

Added mpipe.min-buckets, which defaults to 256, so if the requested number
of buckets can't be allocated, Suricata will keep dividing by 2 until either
it succeeds in allocating buckets, or reaches the minimum number of buckets
and fails.

Passes both regressions:
https://buildbot.suricata-ids.org/builders/ken-tilera-pcap/builds/2
https://buildbot.suricata-ids.org/builders/ken-tilera/builds/65