rn_addmask
x = rn_addmask(m_arg, 1, head->rnh_treetop->rn_offset);
if ((x = rn_addmask(netmask, 0, top->rn_offset)) == 0)
if ((x = rn_addmask(netmask, 1, head_off)) == 0)
struct radix_node *rn_addmask(void *, int, int);