iwlwifi: mvm: don't wait for session protection to start

Now that mac80211 no longer starts the auth/assoc
timeouts when it transmits the frame, but only when
the frame status arrives, we no longer need to wait
for the session protection time event to start, we
can schedule it and enqueue the auth/assoc frame
right away. This reduces the amount of time we block
mac80211's workqueue.

Also, since now we no longer need different behavior
for session protection and P2P time events, refactor
the code to have just a common implementation.

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