iwlwifi: mvm: refactor the way fw_key_table is handled

Instead of keeping the fw_key_table bits set when the keys are removed
(i.e. in D3 entry or HW_RESTART flows), clear them and set them again
only when the keys have been successfully re-added.  This makes the
bitmask more closely tied to the actual firmware programming.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>