iwlwifi: mvm: align locking in D3 test debugfs

Since commit a05829a7 ("cfg80211: avoid holding the RTNL when
calling the driver") we're not only holding the RTNL when going
in and out of suspend, but also the wiphy->mtx. Add that to the
D3 test debugfs in iwlwifi since it's required for various calls
to mac80211.

Fixes: a05829a7 ("cfg80211: avoid holding the RTNL when calling the driver")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Fixes: a05829a7 ("cfg80211: avoid holding the RTNL when calling the driver")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20220129105618.fcec0204e162.Ib73bf787ab4d83581de20eb89b1f8dbfcaaad0e3@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>