test

            // a bridge takes members as they are (up): it goes up first, so

            // the new port forwards at once (no STP: no listening/learning)

            setLinkUp(master);

            // a bond in a bridge: the bridge keeps the bond's MAC for good

            // (else it takes the lowest of its ports' and changes with them),

            // so switches and ARP caches see the same address as before

            std::error_code ec;

            if (std::filesystem::exists("/sys/class/net/" + ifname + "/bonding", ec) &&

                readSysfs(master, "addr_assign_type") != "3" /* NET_ADDR_SET */)

            // the bridge keeps its first member's (or a bond's) MAC for good:

            // else it takes the lowest of its ports' and changes with them --

            // with every container's veth that comes and goes -- and

            // switches and ARP caches lose the host for a while

            if (readSysfs(master, "addr_assign_type") != "3" /* NET_ADDR_SET */)

                setLinkAddress(master, readSysfs(ifname, "address"));

            if (!setMaster(ifname, master))

                std::cerr << "[syslite/net] " << ifname << ": cannot add it to " << master << std::endl;