Basic module for net instrumentation

This module aims at recording network events and relate them to user-space
processes. It includes the following instrumentation.

 * records connect and accept to match client and server socks objects
 * records sock create, clone and delete
 * records hints about TCP packets sent and received

Instrumentation is performed with kprobe, by overriding the netfamilly IPV4 and
by means of netfilter hooks.
Fix compilation issue with socket statedump
Fix declaration warning
Add fields to tcp probe: checksum, window, flags

Thanks to Geneviève Bastien for this patch.
Work around sock_from_file in older kernel

In older kernel < 3.6 function sock_from_file is not exported. Copy the
function to make it work.
Fix TCP flags endianness

Shift TCP flags according to endianness.

Thanks to Genevieve Bastien for this patch

Signed-off-by: Francis Giraldeau <francis.giraldeau@gmail.com>