iwlwifi: mvm: extend session protection on association

When we receive an association response, a significant amount
of time might have passed since we sent the corresponding
association request (mac80211 will wait up to 500ms for the TX
and then 100ms for the response after ACK was received). But
the time event is touched only when we send the assoc request,
so it might not have much time remaining, more easily causing
the (dreaded)

  No beacon heard and the session protection is over already...

message.

Refactor iwl_mvm_mac_mgd_prepare_tx() and split out a new
function iwl_mvm_protect_assoc(), and call it on successful
association to extend the time event to the minimum time if
necessary.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20211024181719.411c174d9e5e.I03c701c2e9e6788f34546e538264763db0ab30ef@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>