mac80211: mesh data structures and first mesh changes

Includes integration in struct sta_info of mesh peer link elements, previously
on their own mesh peer link table.

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>