We make oldconfig every time when a new kernel arrives, but
if we don't have such a device(I guess this is the most common
case for a new device), the default value should be 'n' so
that the kernel size we build doesn't grow up too much quickly.
For anyone who has the device, it is OK for them to turn it on
by themselves.

Cc: "John W. Linville" <linville@tuxdriver.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>