libnetfilter_queue do projeto netfilter parece o seguinte: do netfilter.org:
libnetfilter_queue is a userspace library providing an API to packets that have been queued by the kernel packet filter. It is is part of a system that deprecates the old ip_queue / libipq mechanism.
Eu coloco pacotes em uma fila com:
sudo iptables -I FORWARD (parameters) -j NFQUEUE --queue-num x
e com libnetfilter_queue eu posso acessar os pacotes armazenados na fila acima.