refcnt_read
assert(refcnt_read(&rt->rt_refcnt) == 0);
refs = refcnt_read(&rt->rt_refcnt);
assert(refcnt_read(&rt->rt_refcnt) == refs - 1);
KASSERT(refcnt_read(&rt->rt_refcnt) >= 1);
rtm->rtm_rmx.rmx_refcnt = refcnt_read(&rt->rt_refcnt) - 1;
unsigned int refcnt_read(const struct refcnt *);
#define refcnt_shared(_r) (refcnt_read((_r)) > 1)