iptun_enter
static int iptun_enter(iptun_t *);
if ((err = iptun_enter(iptun)) == 0) {
if (iptun_enter(iptun) == 0) {
if ((err = iptun_enter(iptun)) == 0) {
if ((err = iptun_enter(iptun)) != 0)
if ((err = iptun_enter(iptun)) != 0)
err = iptun_enter(*iptun);