mac80211: ibss: use beacon_data struct for beacon and probe response

Instead of having an SKB all the time, use a beacon_data struct
with just the information required. This also allows removing a
synchronize_rcu() and using kfree_rcu() instead.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --cc net/mac80211/ibss.c
Simple merge

diff --cc net/mac80211/ieee80211_i.h
Simple merge

diff --cc net/mac80211/tx.c
Simple merge