rn_addmask
tm = rn_addmask(m_arg, 1, head->rnh_treetop->rn_off);
struct radix_node *rn_addmask(void *, int, int);
if ((tm = rn_addmask(n_arg, 0, top->rn_off)) == 0)
if ((tm = rn_addmask(netmask, 1, off)) == NULL)