CANP_NO_LOOPBACK
if ((sender_canp->canp_flags & CANP_NO_LOOPBACK) != 0) {
optval = (canp->canp_flags & CANP_NO_LOOPBACK) ? 0 : 1;
canp->canp_flags &= ~CANP_NO_LOOPBACK;
canp->canp_flags |= CANP_NO_LOOPBACK;