__svc_get_door_ucred
err = __svc_get_door_ucred(trans, uc) == FALSE;
err = __svc_get_door_ucred(xprt, uc) == FALSE;
err = __svc_get_door_ucred(trans, ucp) == FALSE;
extern bool_t __svc_get_door_ucred(const SVCXPRT *, ucred_t *);