wifi: iwlwifi: mvm: check link more carefully

Some cases of restart crashing here have been reported,
while we figure out where this is going wrong, check
the link more carefully to avoid the crash.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230830112059.2b81f52ce18e.I8f3b1962013107e2d7491d817c3349359341c6ee@changeid


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