net/tap: rework scripts handling Simplify handling scripts: parse all these "no" and '\0' once, and then keep simpler logic for net_tap_open() and net_init_tap_one(): NULL means no script to run, otherwise run script. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> Reviewed-by: Maksim Davydov <davydov-max@yandex-team.ru> Signed-off-by: Jason Wang <jasowang@redhat.com>