iwlwifi: mvm: restructure scan parameters calculation

Some scan parameters should be dependent on traffic conditions.
Centralize conditions verification in one function and obtain
scan max out-of-channel and suspend time in that new function.
Rely on bound interfaces indication instead of association state
to calculate scan parameters. If no bound interfaces use default
values for out-of-channel and suspend time parameters.

Additionally, get rid of NL80211_SCAN_FLAG_LOW_PRIORITY checks
since no use case for this exists so far.

Signed-off-by: Alexander Bondar <alexander.bondar@intel.com>
[reword commit log a bit]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>