iwlwifi: mvm: suppress key error messages in AP mode

In AP mode, don't attempt to program GTKs into the
device, they're used for TX only so not needed and
programming them causes error messages. Also, in
this case and if key programming fails, avoid trying
to remove the key that isn't present later.

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