qa: build unshared nfct environment

nssocket forks and change netns pre-establishd by ip(8),
serves its socket descriptor to parent via nssocket().
Since this socket is isolated, I think it is suitable for
test. see example, ct_echo_event.c and ct_echo_event.sh

Signed-off-by: Ken-ichirou MATSUZAWA <chamas@h4.dion.ne.jp>