ipfw_link
if (V_fw_enable && (error = ipfw_link(AF_INET, false)) != 0)
if (V_fw6_enable && (error = ipfw_link(AF_INET6, false)) != 0)
if (V_fwlink_enable && (error = ipfw_link(AF_LINK, false)) != 0)
error = ipfw_link(af, newval == 0 ? true : false);