iwlwifi: mvm: limit non-low-latency binding scheduling duration

Limit the scheduling duration of bindings without a low-latency
interface in the firmware, this prevents those bindings from
occupying the medium for a period of time longer than what we
want for the other interfaces in low-latency mode.

As older firmware doesn't do anything with the max_duration field
and ignores it completely, there's no need for a firmware flag.

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