ipsec4_process_packet
error = ipsec4_process_packet(m, sp->req, &_mtu);
int ipsec4_process_packet(struct mbuf *, const struct ipsecrequest *, u_long *);
return ipsec4_process_packet(m, isr->next, NULL);
error = ipsec4_process_packet(m, sp->req, &sa_mtu);