mac80211: mesh changes to the MLME

This includes support for mesh network scanning. The ugly code in
ieee80211_sta_scan_result() is my approach to work around wext. This has been
tested with wireless tools version 29 and works as expected (the new interface
mode is just not shown).
Signed-off-by: Luis Carlos Cobo <luisca@cozybit.com>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>