cfg80211/mac80211: Revert "move information element parsing logic to cfg80211"

No other driver ever ended up using this, and
the commit forgot to move the prototype so no
driver could have used it. Revert it, if any
driver shows up and needs it it can be moved
again, but until then it's more efficient to
have it in mac80211 where the only user is.

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