wifi: mac80211: provide a helper to fetch the medium synchronization delay

There are drivers which need this information.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230604120651.b1043f3126e2.Iad3806f8bf8df07f52ef0a02cc3d0373c44a8c93@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>