netdevconf: remove redundant and unsafe check

we don't need this check as just after it we have:
if (ret)
	break;
which safely unpackes nde, and closes nlsk and img in case of error

ps: sorry for inconveniences caused by my patchset
Signed-off-by: Pavel Tikhomirov <ptikhomirov@odin.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>