class_to_msl
msl = (2 * class_to_msl(ctl->clidx) * 1000) / PR_SLOWHZ; // msec
ctl = vtw_control(AF_INET, class_to_msl(cp->msl_class));
ctl = vtw_control(AF_INET6, class_to_msl(cp->msl_class));
ctl = vtw_control(af, msl ? msl : class_to_msl(msl_class));