wext: default to y

The way I initially thought we could do wireless extensions
is by making all the compat code in cfg80211 be independent
of CONFIG_WIRELESS_EXT, but this is turning out to not be
feasible. Therefore, fix the Kconfig help text and make the
option default to yes, so people won't get a nasty surprise
when mac80211 will get rid of its 'select WIRELESS_EXT' any
time now.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>