wifi: cfg80211: refactor 6 GHz AP power type parsing

Add cfg80211_get_6ghz_power_type() to parse the 6 GHz
power type from a given set of elements, which is now
only inside cfg80211_6ghz_power_type_valid().

Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://msgid.link/20240523120945.84cdffd94085.I76f434ee12552e8be91273f3b2d776179eaa62f1@changeid


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