iwlwifi: dvm: don't send zeroed LQ cmd

When the stations are being restored because of unassoc
RXON, the LQ cmd may not have been initialized because it
is initialized only after association.
Sending zeroed LQ_CMD makes the fw unhappy: it raises
SYSASSERT_2078.

Cc: stable@vger.kernel.org
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
[move zero_lq and make static const]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>