i40e: fix endless loop under rtnl

The loop in i40e_get_capabilities can never end. The problem is that
although i40e_aq_discover_capabilities returns with an error if there's
a firmware problem, the returned error is not checked. There is a check for
pf->hw.aq.asq_last_status but that value is set to I40E_AQ_RC_OK on most
firmware problems.

When i40e_aq_discover_capabilities encounters a firmware problem, it will
encounter the same problem on its next invocation. As the result, the loop
becomes endless. We hit this with I40E_ERR_ADMIN_QUEUE_TIMEOUT but looking
at the code, it can happen with a range of other firmware errors.

I don't know what the correct behavior should be: whether the firmware
should be retried a few times, or whether pf->hw.aq.asq_last_status should
be always set to the encountered firmware error (but then it would be
pointless and can be just replaced by the i40e_aq_discover_capabilities
return value). However, the current behavior with an endless loop under the
rtnl mutex(!) is unacceptable and Intel has not submitted a fix, although we
explained the bug to them 7 months ago.

This may not be the best possible fix but it's better than hanging the whole
system on a firmware bug.

Fixes: 56a62fc8 ("i40e: init code and hardware support")
Tested-by: Stefan Assmann <sassmann@redhat.com>
Signed-off-by: Jiri Benc <jbenc@redhat.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Dave Switzer <david.switzer@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/i40e/i40e_main.c

@@ -10113,7 +10113,7 @@ static int i40e_get_capabilities(struct i40e_pf *pf,
 		if (pf->hw.aq.asq_last_status == I40E_AQ_RC_ENOMEM) {
 			/* retry with a larger buffer */
 			buf_len = data_size;
-		} else if (pf->hw.aq.asq_last_status != I40E_AQ_RC_OK) {
+		} else if (pf->hw.aq.asq_last_status != I40E_AQ_RC_OK || err) {
 			dev_info(&pf->pdev->dev,
 				 "capability discovery failed, err %s aq_err %s\n",
 				 i40e_stat_str(&pf->hw, err),