iwlwifi: mvm: check minimum temperature notification length

This notification will be extended with extra data, so just
check that it has a minimum length, not the exact length;
we might later add handling for the extra fields added and
have more code to handle both versions.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>