mac80211: add vif to flush call

This will allow the low level driver to make decision based
on the vif such as queues etc...
Since the vif might be NULL, we can't add it to the tracing
functions.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
[fix staging rtl8821ae driver]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>