[PATCH] dynamic calculation of event message size for ctnetlink

This patch adds dynamic message size calculation for ctnetlink. This
reduces CPU consumption since the overhead in the message trimming
is removed.

Note that if we create an entry in the connection tracking for
any layer 3 or 4 protocol helper that is not loaded, eg. SCTP,
DCCP, IPv6, the calculated size is not accurate.

Based on a suggestion from Patrick McHardy.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

-- 
"Los honestos son inadaptados sociales" -- Les Luthiers