pp fixes v0

cc @ken-tilera

Fix issues with pcap autofp modes. As the 'cnt' passed to pcap_dispatch was now always 0, the pcap loops would not return until EOF, causing us not to wait for PacketPoolWait in case of empty pools. This lead to allocing new packets at line rate.

Also, fix a pending list insert issue that caused the engine to get stuck. Pool would be empty and all threads sleeping.