mac80211: move TDLS data to mgd private part

We can only be a station for TDLS connections. Also fix a bug where
a delayed work could be left scheduled if the station interface was
brought down during TDLS setup.

Signed-off-by: Arik Nemtsov <arikx.nemtsov@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>