add support to related connections via ctnetlink

This patch adds support to relate a connection to an
existing master
connection. This patch is used by conntrackd to correctly
replicate
related connections.

Signed-off-by: Pablo Neira Ayuso <pablonetfilter.org>

-- 
"Será preciso viajar por los ojos de los idiotas"
-- Poeta en Nueva York
-- Federico García Lorca.

Pablo Neira Ayuso wrote:
> This patch adds support to relate a connection to an
existing master
> connection. This patch is used by conntrackd to
correctly replicate
> related connections.
>   

Queued for 2.6.24, thanks Pablo.