mac_socket_check_receive
error = mac_socket_check_receive(active_cred, so);
error = mac_socket_check_receive(fp->f_cred, so);
error = mac_socket_check_receive(td->td_ucred, so);
error = mac_socket_check_receive(td->td_ucred, so);
int mac_socket_check_receive(struct ucred *cred, struct socket *so);