wifi: iwlwifi: mvm: skip inactive links

When iterating station links, skip the links that are not
yet active by checking for mvmvif->link[] existence.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230329100039.bd9b4e64c478.Ie21422c3bf2589d22942c3c57d26e6330d2e3afc@changeid


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