SPPP_IPCP_OPT_PRIMDNS
sp->ipcp.opts &= ~(1 << SPPP_IPCP_OPT_PRIMDNS);
sp->ipcp.opts |= (1 << SPPP_IPCP_OPT_PRIMDNS);
if (sp->ipcp.opts & (1 << SPPP_IPCP_OPT_PRIMDNS)) {