wifi: iwlwifi: mvm: rework active links counting

Remove fw_active_links_num counter since we now have a bitmap of
active links in vif. Also, update link activation status only when
LINK_CONTEXT_MODIFY_ACTIVE bit set in changes parameter.

Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230329100040.1ecfb27b6b84.I3a5e0bc32b3728e4caae8a231bc3f04ea1d89cad@changeid


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