CRIU uses iptables rules to block tcp connections and
if rules are added at the tail of the chain, other rules
can accept packets which have to be blocked.

travis-ci: success for series starting with [01/21] build: install libnet-dev
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>