vconfig: remove /proc/net/vlan/config check

vconfig: remove /proc/net/vlan/config check

In original implementation /proc/net/vlan/config check only prints warning
and does not exit. Busybox version exits if this file is not found and this
prevents kernel module autoloading to work.
I think it is safe to remove this check since ioctl() call will fail
(with proper
error code) anyway if 802.1q module is not loaded (or autoloading is off).

Signed-off-by: Paulius Zaleckas <paulius.zaleckas@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>