net/wireless/Kconfig: clarify the description for CONFIG_WIRELESS_EXT_SYSFS

Current setup with hal and NetworkManager will fail to work
without newest hal version with this config option disabled.

Although this will solve itself by time, at the moment it is
dishonest to say that we don't know any software that uses it,
if there are many many people relying on old hal versions.

Signed-off-by: Florian Mickler <florian@mickler.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>