Infrastructure libnfnetlink / libctnetlink

libnfnetlink
- provides low layer communications between netlink socket and high layer
  library
- provides generic functions to create and parse nf_attr's
- hides all details of netlink socket
- provides open/close/receive/listen functions only to be used by other 
  libraries (libctnetlink/libpkttnetlink/...)


libctnetlink:
- provides high layer interface for applications interfacing with conntrack
  kernel code
- event messages (to be implemented)
- reading and deleting ip_conntrack's
- reading, deleting and creating ip_conntrack_expect's





Layout of nfnetlink data packet


struct nlmsghdr		- netlink internal 
struct nfgenmsg		- information about