busybox

ifplugd: if SIOCSIFFLAGS fails with ENODEV, don't die

Some user managed to hit a race where iface is gone between SIOCGIFFLAGS
and SIOCSIFFLAGS (!). If SIOCSIFFLAGS fails, treat it the same as failed
SIOCGIFFLAGS

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>