ec_start
void ec_start(struct ifnet *);
ifp->if_start = ec_start;
ec_start(ifp);
ep->e_start_lo = ecp->ec_start & 0xffffffff;
ep->e_start_hi = ecp->ec_start >> 32 & 0xffff;
ecp->ec_start = (daddr_t)ep->e_start_hi << 32 | ep->e_start_lo;
daddr_t ec_start; /* extent start */